The stream selection state wasn't improved. I didn't realize this messed
with caches. All in all, just not a good idea. Back to drawing board I
guess.
This reverts commit f40bbfec4f.
This replaces the previous commit and makes more sense. The internal
demux marked tracks as eager depending on their type and for subtitles
it would always lazily read them unless there happened to be no
available av stream. However, we want the sub stream to be eager if the
player is paused. The existing subtitle is still preserved on the
screen, but if the user changes tracks that's when the problem occurs.
So to handle this case, propagate the mpctx->paused down to the stream
selection logic. This modifies both demuxer_refresh_track and
demuxer_select_track to take that boolean value. A few other parts of
the player use this, but we can just assume false there (no change in
behavior from before) since they should never be related to subtitles.
The core player code is aware of its own state naturally, and can always
pass the appropriate value so go ahead and do so. When we change the
pause state, a refresh seek is done on all existing subtitle tracks to
make sure their eager state is the appropriate value (i.e. so it's not
still set to eager after a pause and a track switch). Slightly invasive
change, but it works with the existing logic instead of going around it
so ultimately it should be a better approach. We can additionally remove
the old force boolean from sub_read_packets since it is no longer
needed.
This exposes whether a video track is detected as an image, which is
useful for profile conditions, property expansion and lavfi-complex.
The lavf demuxer sets image to true when the existing check detects an
image.
When the lavf demuxer fails, the mf one guesses if the file is an image
by its extension, so sh->image is set to true when the mf demuxer
succeds and there's only one file.
The mkv demuxer just sets image to true for any attached picture.
The timeline demuxer just copies the value of image from source to
destination. This sets image to true for attached pictures, standalone
images and images added with !new_stream in EDL playlists, but it is
imperfect since you could concatenate multiple images in an EDL playlist
(which should be done with the mf demuxer anyway). This is good enough
anyway since the comment of the modified function already says it is
"Imperfect and arbitrary".
Unfortunately, this functionality in large part based on a struct
member that was made private in FFmpeg/FFmpeg@7489f63281
in May. Unfortunately, this was not noticed during review.
This reverts commit 0862664ac9.
This exposes whether a video track is detected as an image. This is
useful for profile conditions, property expansion and lavfi-complex, and
is more accurate than any detection even Lua scripts can perform, since
they can't differentiate between images and videos without container-fps
and audio and with duration 1 (which is the duration set by the mf
demuxer with the default --mf-fps=1).
The lavf demuxer image check is moved to where the number of frames is
available for comparison, and is modified to check the number of frames
and duration instead of the video codec. This doesn't misdetect videos
in a codec commonly used for images (e.g. mjpeg) as images, and can
detect images in a codec commonly used for videos (e.g. 1-frame gifs).
pix files are also now detected as images, while before they weren't
since the condition was checking if the AVInputFormat name ends with
_pipe, and alias_pix doesn't.
Both nb_frames and codec_info_nb_frames are checked because nb_frames is
0 for some video codecs (hevc, av1, vc1, mpeg1video, vp9 if forcing
--demuxer=lavf), and codec_info_nb_frames is 1 for others (mpeg, mpeg4,
wmv3).
The duration is checked as well because for some uncommon codecs and
containers found in FFMpeg's FATE suite, libavformat returns nb_frames =
0 and codec_info_nb_frames = 1. For some of them it even returns
duration = 0, so they are blacklisted in order to never be considered
images.
The extra codecs that would have to be blacklisted without checking the
duration are AV_CODEC_ID_4XM, AV_CODEC_ID_BINKVIDEO,
AV_CODEC_ID_DSICINVIDEO, AV_CODEC_ID_ESCAPE130, AV_CODEC_ID_MMVIDEO,
AV_CODEC_ID_NUV, AV_CODEC_ID_RL2, AV_CODEC_ID_SMACKVIDEO and
AV_CODEC_ID_XAN_WC3, while the containers are film-cpk, ivf and ogg.
The lower limit for duration is 10 because that's the duration of
1-frame gifs.
Streams with codec_info_nb_frames 0 are not considered images because
vp9 and av1 have nb_frames = 0 and codec_info_nb_frames = 0, and we
can't rely on just the duration to detect them because they could be
livestreams without an initial duration, and actually even if we could
for these codecs libavformat returns huge negative durations like
-9223372036854775808.
Some more images in the FATE suite that are really frames cut from a
video in an uncommon codec and container, like cine/bayer_gbrg8.cine,
could be detected by allowing codec_info_nb_frames = 0, but then any
present and future video codec with nb_frames = 0 and
codec_info_nb_frames = 0 would need to be added to the blacklist. Some
even have duration > 10, so to detect these images the duration check
would have to be removed, and all the previously mentioned extra codecs
and containers would have to be added added to the blacklists, which
means that images that use them (if they exist anywhere) will never be
detected. These FATE images aren't detected as such by mediainfo either
anyway, nor can a Lua script reliably detect them as images since they
have container-fps and duration > 0 and != 1, and you probably will
never see files like them anywhere else.
For attached pictures the lavf demuxer always set image to true, which
is necessary because they have duration > 10. There is a minor change in
behavior for which audio with attached pictures now has mf-fps as
container-fps instead of unavailable, but this makes it consistent with
external cover art, which was already being assigned mf-fps.
When the lavf demuxer fails, the mf one guesses if the file is an image
by its extension, so sh->image is set to true when the mf demuxer
succeds and there's only one file.
Even if you add a video's file type to --mf-type and open it with the mf
protocol, only the first frame is used, so setting image to true is
still accurate.
When converting an image to the extensions listed in demux/demux_mf.c,
tga and pam files are currently the only ones detected by the mf demuxer
rather than lavf. Actually they are detected with the image2 format, but
it is blacklisted; see d0fee0ac33.
The mkv demuxer just sets image to true for any attached picture.
The timeline demuxer just copies the value of image from source to
destination. This sets image to true for attached pictures, standalone
images and images added with !new_stream in EDL playlists, but it is
imperfect since you could concatenate multiple images in an EDL playlist
(which should be done with the mf demuxer anyway). This is good enough
anyway since the comment of the modified function already says it is
"Imperfect and arbitrary".
Exposed by commit b56e2efd5f. demux_timeline reported a bogus EOF if
"parallel" streams were used. If a virtual source reported EOF, it was
propagated as global EOF, without serving packets of other virtual
sources that have not ended yet.
Fix this by not reporting global EOF just because a source has not
returned a packet. Instead make the reader retry by returning no packet
and no EOF state, which will call d_read_packet() again with a different
source. Rely on the eof_reached flags to signal global EOF.
Since eof_reached is now more important, set it in a certain other case
when it apparently should have been set. do_read_next_packet()'s return
value is now ignored, so get rid of it.
Until now, delay-loading was for files with single tracks only
(basically what DASH and HLS like to expose, so adaptive streaming and
codec selection becomes easier - for sites, not for us). But they also
provide some interleaved versions, probably for compatibility. Until
now, we were forced to eagerly load it (making startup slightly slower).
But there is not much missing. We just need a way to provide multiple
metadata entries, and use them to represent each track.
A side effect is now that the "track_meta" header can be used for normal
EDL files too.
Now this was stupid. To seek a source, it obviously has to be opened...
so just don't try to seek any unused source. If the track is actually
selected during playback, a seek to the correct position is performed
anyway.
ytdl_hook.lua can do this with all_formats and when delay_open is used,
and if the source stream actually contains both audio and video. In this
case, it might accidentally hide a media type completely, or waste
bandwidth (if the stream has true interleaved audio/video). So it's
important to warn.
Add something that will access an URL embedded in EDL only when the
track it corresponds to is actually selected. This is meant to help with
ytdl_hook.lua and to improve loading speeds.
In theory, all this stuff is available to any mpv user, but discourage
using it, as it's so specialized towards ytdl_hook.lua, that there's
danger we'll just break this once ytdl_hook.lua stops using it, or
similar.
Mostly untested.
The timeline stuff has messed up memory management because there are no
clear ownership rules between a some demuxer instances (master or
demux_timeline) and the timeline object itself.
This is another subtle problem that happened: apparently,
demux_timeline.open is supposed to take over ownership of timeline, but
only on success. If it fails, it's not supposed to free it. It didn't
follow this, which lead to a double-free if demux_timeline.open failed.
The failure path in demux.c calls both timeline_destroy() and
demux_timeline.close on failure.
Move them around in the source code to get rid of the forward
declarations. Other than rearranging the lines and removing the 2
forward declarations, there are no other changes at all.
mpv has a very weak and very annoying policy that determines whether a
playlist should be used or not. For example, if you play a remote
playlist, you usually don't want it to be able to read local filesystem
entries. (Although for a media player the impact is small I guess.)
It's weak and annoying as in that it does not prevent certain cases
which could be interpreted as bad in some cases, such as allowing
playlists on the local filesystem to reference remote URLs. It probably
barely makes sense, but we just want to exclude some other "definitely
not a good idea" things, all while playlists generally just work, so
whatever.
The policy is:
- from the command line anything is played
- local playlists can reference anything except "unsafe" streams
("unsafe" means special stream inputs like libavfilter graphs)
- remote playlists can reference only remote URLs
- things like "memory://" and archives are "transparent" to this
This commit does... something. It replaces the weird stream flags with a
slightly clearer "origin" value, which is now consequently passed down
and used everywhere. It fixes some deviations from the described policy.
I wanted to force archives to reference only content within them, but
this would probably have been more complicated (or required different
abstractions), and I'm too lazy to figure it out, so archives are now
"transparent" (playlists within archives behave the same outside).
There may be a lot of bugs in this.
This is unfortunately a very noisy commit because:
- every stream open call now needs to pass the origin
- so does every demuxer open call (=> params param. gets mandatory)
- most stream were changed to provide the "origin" value
- the origin value needed to be passed along in a lot of places
- I was too lazy to split the commit
Fixes: #7274
The demuxer_id (exported in as "src-id" property) is supposed to be the
native stream ID, as it exists in the file, or -1 if that does not exist
(actually any negative value), or if it is unknown.
Until now, an ID was made up if it was missing. That seems like strange
non-sense, and I can't find the reason why it was done. But it was
probably for convenience by the EDL stuff or so.
Stop doing this. Fortunately, the src-id property was documented as
being unavailable if the ID is not known. Even the code for this was
present, it was just inactive until now. Extend input.rst with some
explanations.
Also fixing 3 other places where negative demuxer_id was ignored or
avoided.
In pseudo-DASH mode, we may have no real streams opened until the
demuxer layer is fully loaded and playback actually starts. The only
hint that the stream is from network is, at that point, the init
segment, which is only opened as stream, and then separately as demuxer
(which is dumb but happened to fit the internal architecture better).
So just propagate the flags from the init segment stream. Seems like an
annoyance, but doesn't hurt that much I guess. (Until someone gets the
idea to pass the init segment data inline or so, but nothing does that.)
The sample link in the linked issue will probably soon switch to another
format, because that service always does this after recent uploads or
so.
Fixes: #7038
Before this commit, EDL or CUE files did not properly enable the cache
if they were on "slow" media (stream->streaming==true). This happened
because the stream is unset for demux_timeline, so the streaming flag
could not be queried anymore.
Fix this by adding this flag to struct demuxer, and propagate it exactly
like the is_network flag. is_network is not used for checking the cache
options anymore, and its main function seems to be something else.
Normal http streams set the streaming flag already.
This should fix#6958.
Remove the duplicated creation of the first range. Explicitly destroy
ranges, including the last one on final deinit.
It looks like this also fixes a leak of removed range structs, which was
never noticed because they're so small, and were freed on final deinit
due to having the demuxer as talloc parent.
This improves upon the previous commit too (that change should have
been part of it I guess). Sub-demuxers (demux_timeline only) now
automatically don't use the cache (like it was intended by the previous
commit). The cache is "initialized" (or disabled) last in the recursive
call chain, which is messy, but this sub demuxer stuff FUCKING SUCKS, as
mentioned in the previous commit message. This would be no problem if
the caching layer and actual demuxer implementations were separate.
Most of this change has no purpose. Might make (de-)initialization of
further cache exerpiments simpler.
If you have a EDL stream with separate sources for audio and video
stream (like ytdl_hook now creates), you can get the problem that the
video stream seeks to a different position than audio due to different
key frame granularity.
In particular, if you seek backward, the video might undershoot the seek
target by a lot. Then video will resume from an earlier position than
audio, and the player plays silence. This is annoying.
Fix this by explicitly implementing a heuristic to detect separate
audio/video streams, determining where a video seek ends up, and then
seeking the audio stream to the video destination. This also makes sure
to not seek audio with SEEK_FORWARD, so it will always seek before the
video position. Non-precise seeks still skip audio to the video target,
so this helps with ensuring that audio is present at the final seek
target.
The implementation is very annoying, because the only way to determine
the seek target is to actually read a packet. Thus a 1-packet queue
needs to be added. In theory, we could get the seek target from the
index of the video file (especially if it's mp4), but libavformat does
not have public API that exports this index, so we're stuck with this
roundabout generic method.
Note that this is only for non-precise seeks. If precise seeks are done,
the problem is handled by the frontend by skipping unwanted video
frames. But non-precise seeking should still work. (Personally I prefer
non-precise seek mode by default because they're still significantly
faster.)
It also needs to be said that this is the 4th implementation of this
seek adjustment thing in mpv. The 1st implementation is in the frontend
(look for MPContext.seek_slave). This works only if the external audio
stream is known as such on the frontend level. The 2nd implementation is
in the demuxer level packet cache (top of execute_cache_seek()). This is
similar to code that any demuxer needs to handle non-precise seeks
sufficiently nicely. The 3rd is in demux_mkv.c. Since mkv is an
interleaved format, this implementation mostly consists on trying to
pick index entries for video packets if a video stream is selected.
Maybe these "redundant" implementations could be avoided by exposing
separate streams through the demuxer API (and making them individually
seekable) or something like this, but this is messy and not without
problems for multiple reasons. So for now this commit is the best way to
fix the observed behavior.
Instead of just using "edl/" for the file format, report mkv_oc if it's
generated from ordered chapters, "cue/" if from .cue, "multi/" if it's
from EDL but only for adding separate streams, "dash/" if it's from EDL
but only using the DASH hack, and "edl/" for everything else.
The EDL variants are mostly special-cased to the variants the ytdl
wrapper usually generates.
This has no effect other than what the command.c file-format property
returns.
Remove the singly linked list hack, replace it with a slightly more
proper data structure. This probably gets rid of a few minor bugs along
the way, caused by the awkward nonsensical sharing/duplication of some
fields.
Another change (because I'm touching everything related to timeline
anyway) is that I'm removing the special semantics for parts[num_parts].
This is now strictly out of bounds, and instead of using the start time
of the next/beyond-last part, there is an end time field now.
Unfortunately, this also requires touching the code for cue and mkv
ordered chapters. From some superficial testing, they still seem to
mostly work.
One observable change is that the "no_chapters" header is per-stream
now, which is arguably more correct, and getting the old behavior would
require adding code to handle it as special-case, so just adjust
ytdl_hook.lua to the new behavior.
Used by the next commit. It mostly exposes part of mp4_dash
functionality. It actually makes little sense other than for ytdl
special-use. See next commit.
Normal EDL needs to clip packets coming from the underlying demuxer to
the segment range (including complicated stuff due to frame reordering).
This is unwanted In pseudo-DASH mode. A broken or subtly incorrect
manifest would lead to "bad stuff" happening. The intention of the
pseudo-DASH mode is to literally concatenate fragments.
demux_timeline doesn't do any transport accesses itself. The slave
demuxers do this (these will actually access the stream layer and
perform e.g. network accesses). As a consequence, demux_timeline always
reported 0 bytes read, and network speed display didn't work.
Fix this by awkwardly reporting the amount of read bytes upwards. This
is not very nice, and requires explicit calls whenever the slave "might"
have read data.
Due to the way the reporting is done, it only works if the slaves do not
run demuxer threads, which makes things even less nice. (Fortunately
they don't anyway, because it would be a waste of resources.) Some
identifiers contain the word "hack" as a warning.
Some of the stupidity comes from the fact that demux.c itself resets the
stats randomly in order to calculate the bytes_per_second value, which
is useless for a slave, but of course is still done, because demux.c
itself is not aware of whether it's on the slave or top-level layer.
Unfortunately, this must do.
In theory, the demuxer thread/cache layer should be separated from
demuxer implementations. This would get rid of all the awkwardness and
nonsense. For example, the only threading involved would be the caching
layer, completely separate from demuxers themselves. It'd be the only
thing calculates speed rates for the player frontend, too (instead of
doing it for each demuxer, even if unused).
This commit adds an extension to mpv EDL, which basically allows you to
do the same as --audio-file, --external-file, etc. in a single EDL file.
This is a relatively quick & dirty implementation. The dirty part lies
in the fact that several shortcuts are taken. For example, struct
timeline now forms a singly linked list, which is really weird, but also
means the other timeline using demuxers (cue, mkv) don't need to be
touched. Also, memory management becomes even worse (weird object
ownership rules that are just fragile WTFs). There are some other
dubious small changes, mostly related to the weird representation of
separate streams.
demux_timeline.c contains the actual implementation of the separate
stream handling. For the most part, most things that used to be on the
top level are now in struct virtual_source, of which one for each
separate stream exists. This is basically like running multiple
demux_edl.c in parallel. Some changes could strictly speaking be split
into a separate commit, such as the stream_map type change.
Mostly untested. Seems to work for the intended purpose. Potential for
regressions for other timeline uses (like ordered chapters) is probably
low. One thing which could definitely break and which I didn't test is
the pseudo-DASH fragmented EDL code, of which ytdl can trigger various
forms in obscure situations. (Uh why don't we have a test suite.)
Background:
The intention is to use this for the ytdl wrapper. A certain streaming
site from a particularly brain damaged and plain evil Silicon Valley
company usually provides streams as separate audio and video streams.
The ytdl wrapper simply does use audio-add (i.e. adding it as external
track, like with --audio-file), which works mostly fine. Unfortunately,
mpv manages caching completely separately for external files. This has
the following potential problems:
1. Seek ranges are rendered incorrectly. They always use the "main"
stream, in this case the video stream. E.g. clicking into a cached range
on the OSC could trigger a low level seek if the audio stream is
actually not cached at the target position.
2. The stream cache bloats unnecessarily. Each stream may allocate the
full configured maximum cache size, which is not what the user intends
to do. Cached ranges are not pruned the same way, which creates disjoint
cache ranges, which only use memory and won't help with fast seeking or
playback.
3. mpv will try to aggressively read from both streams. This is done
from different threads, with no regard which stream is more important.
So it might happen that one stream starves the other one, especially if
they have different bitrates.
4. Every stream will use a separate thread, which is an unnecessary
waste of system resources.
In theory, the following solutions are available (this commit works
towards D):
A. Centrally manage reading and caching of all streams. A single thread
would do all I/O, and decide from which stream it should read next. As
long as the total TCP/socket buffering is not too high, this should be
effective to avoid starvation issues. This can also manage the cached
ranges better. It would also get rid of the quite useless additional
demuxer threads. This solution is conceptually simple, but requires
refactoring the entire demuxer middle layer.
B. Attempt to coordinate the demuxer threads. This would maintain a
shared cache and readahead state to solve the mentioned problems
explicitly. While this sounds simple and like an incremental change,
it's probably hard to implement, creates more messy special cases,
solution A. seems just a better and simpler variant of this. (On the
other hand, A. requires refactoring more code.)
C. Render an intersection of the seek ranges across all streams. This
fixes only problem 1.
D. Merge all streams in a dedicated wrapper demuxer. The general demuxer
layer remains unchanged, and reading from separate streams is handled as
special case. This effectively achieves the same as A. In particular,
caching is simply handled by the usual demuxer cache layer, which sees
the wrapper demuxer as a single stream of interleaved packets. One
implementation variant of this is to reuse the EDL infrastructure, which
this commit does.
All in all, solution A would be preferable, because it's cleaner and
works for all external streams in general.
Some previous commit tried to prepare for implementing solution A. This
could still happen. But it could take years until this is finally
seriously started and finished. In any case, this commit doesn't block
or complicate such attempts, which is also why it's the way to go.
It's worth mentioning that original mplayer handles external files by
creating a wrapper demuxer. This is like a less ideal mixture of A. and
D. (The similarity with A. is that extending the mplayer approach to be
fully dynamic and without certain disadvantages caused by the wrapper
would end up with A. anyway. The similarity with D. is that due to the
wrapper, no higher level code needs to be changed.)
The only thing left is the notification for track switching. Just get
rid of that.
There's probably no real reason to get rid of control(), but why not. I
think I was actually trying to do some real work but fuck that.
This code set pkt->stream to a value which I'm not sure whether it's
correct. A recent commit overwrote it with a value that is definitely
correct.
There appears to be an off by one error. No fucking clue whether this
was somehow correct, but applying an apparent fix does not seem to break
anything, so whatever.
Them being separate is just dumb. Replace them with a single
demux_free() function, and free its stream by default. Not freeing the
stream is only needed in 1 special case (demux_disc.c), use a special
flag to not free the stream in this case.
It seems like there's nothing stopping from sub-demuxers from keeping
packets in the cache, even if it's completely pointless. The top-most
demuxer (demux_timeline) already takes care of caching, so sub-demuxers
only waste space and time with this.
Add a function that can disable the packet cache even at runtime and
after packets are read. (It's not clear whether it really can happen
that packets are read before demux_timeline gets the sub-demuxers, but
there's no reason to make it too fragile.) Call it on all sub-demuxers.
For this to work, it seems we have to move the code for setting the
seekable_cache flag to before demux_timeline is potentially initialized,
because otherwise the cache would be reenabled if the demuxer triggering
timeline support is a timeline segment itself (e.g. ordered chapters).
Fully fixes behavior of the files mentioned in the previous commit. Will
probably lead to worse behavior if someone tries to fix real video and
cover art tracks, but that's a broken fringe case anyway.
The new_segment field was used to track the decoder data flow handler of
timeline boundaries, which are used for ordered chapters etc. (anything
that sets demuxer_desc.load_timeline). This broke seeking with the
demuxer cache enabled. The demuxer is expected to set the new_segment
field after every seek or segment boundary switch, so the cached packets
basically contained incorrect values for this, and the decoders were not
initialized correctly.
Fix this by getting rid of the flag completely. Let the decoders instead
compare the segment information by content, which is hopefully enough.
(In theory, two segments with same information could perhaps appear in
broken-ish corner cases, or in an attempt to simulate looping, and such.
I preferred the simple solution over others, such as generating unique
and stable segment IDs.)
We still add a "segmented" field to make it explicit whether segments
are used, instead of doing something silly like testing arbitrary other
segment fields for validity.
Cached seeking with timeline stuff is still slightly broken even with
this commit: the seek logic is not aware of the overlap that segments
can have, and the timestamp clamping that needs to be performed in
theory to account for the fact that a packet might contain a frame that
is always clipped off by segment handling. This can be fixed later.
Needed for a failed thing, leaving it anyway because it causes no harm
and might be less awkward if struct virtual_stream is possibly extended
anyway in the future.
Seems like most code dealing with this was for setting it in redundant
cases. Now SEEK_BACKWARD is redundant, and SEEK_FORWARD is the odd one
out.
Also fix that SEEK_FORWARD was not correctly unset in try_seek_cache().
In demux_mkv_seek(), make the arbitrary decision that a video stream is
not required for the subtitle prefetch logic to be active. We might want
subtitles with long duration even with audio only playback, or if the
file is used as external subtitle.
Similar purpose as f34e1a0dee.
Somehow this is much more natural too, and needs less code.
This breaks runtime updates to duration. This could easily be fixed, but
no important demuxer does this anyway. Only demux_raw and demux_disc
might (the latter for BD/DVD). For the latter it might actually have
some importance when changing titles at runtime (I guess?), but guess
what, I don't care.
This is more uniform, and potentially gets rid of some past copyrights.
It might be that this subtly changes caching behavior (it seems before
this, it synced to the demuxer if the length was unknown, which is not
what we want.)
We use the metadata provided by youtube-dl to sort-of implement
fragmented DASH streaming.
This is all a bit hacky, but hopefully a makeshift solution until
libavformat has proper mechanisms. (Although in danger of being one
of those temporary hacks that become permanent.)
Instead of enabling it only when a stream-cache is enabled, also try to
enable it independently from that if the demuxer is marked as
is_network.
Also add some code to the EDL code, so EDLs containing network streams
are automatically cached this way.
Extend the OSD info line so that it shows the demuxer cache in this case
(more or less).
I didn't find where or whether options.rst describes how the demuxer
cache is enabled, so no changes there.
This is needed to put the decoders into the correct state. In
particular, decoders will not initialize the current segment without
this flag. The intention of not setting the flag for seeks within the
segments were to avoid costly decoder reinits, but it seems this is
better handled explicitly in the decoder wrappers.
Play a trick to make the packet pos field monotonically increasing over
segment boundaries if the source demuxers return monotonically
increasing pos values. This allows the demuxer to uniquely identify
packets with the pos field, and can do refresh seeks using that.
Normally, the packet pos field is used as a fallback for determining the
playback position if the demuxer returns no proper duration. But
demux_timeline.c always will, and the packet pos fields usually make no
sense in relation to the returned file size anyway if the timeline
source demuxers originate from separate streams.
When switching tracks, we normally have the problem that data gets lost
due to readahead buffering. (Which in turn is because we're stubborn and
instruct the demuxers to discard data on unselected streams.) The
demuxer layer has a hack that re-reads discarded buffered data if a
stream is enabled mid-stream, so track switching will seem instant.
A somewhat similar problem is when all tracks of an external files were
disabled - when enabling the first track, we have to seek to the target
position.
Handle these with the same mechanism. Pass the "current time" to the
demuxer's stream switch function, and let the demuxer figure out what to
do. The demuxer will issue a refresh seek (if possible) to update the
new stream, or will issue a "normal" seek if there was no active stream
yet.
One case that changes is when a video/audio stream is enabled on an
external file with only a subtitle stream active, and the demuxer does
not support rrefresh seeks. This is a fuzzy case, because subtitles are
sparse, and the demuxer might have skipped large amounts of data. We
used to seek (and send the subtitle decoder some subtitle packets
twice). This case is sort of obscure and insane, and the fix would be
questionable, so we simply don't care.
Should mostly fix#3392.
SEEK_HR is interpreted by demux_mkv.c, and enables subtitle preroll by
prefetching additional subtitle pakcets which might overlap with the
seek destination. This should make the case work when segment boundaries
fall into the middle of subtitle events.
This still usually leaves a flicker of at least 1 frame on start,
because dec_sub.c does not ensure that enough subtitles are read before
rendering after a segment switch. (Probably a WONTFIX.)
Dudemanguy