Currently, AVStream contains an embedded AVCodecContext instance, which
is used by demuxers to export stream parameters to the caller and by
muxers to receive stream parameters from the caller. It is also used
internally as the codec context that is passed to parsers.
In addition, it is also widely used by the callers as the decoding (when
demuxer) or encoding (when muxing) context, though this has been
officially discouraged since Libav 11.
There are multiple important problems with this approach:
- the fields in AVCodecContext are in general one of
* stream parameters
* codec options
* codec state
However, it's not clear which ones are which. It is consequently
unclear which fields are a demuxer allowed to set or a muxer allowed to
read. This leads to erratic behaviour depending on whether decoding or
encoding is being performed or not (and whether it uses the AVStream
embedded codec context).
- various synchronization issues arising from the fact that the same
context is used by several different APIs (muxers/demuxers,
parsers, bitstream filters and encoders/decoders) simultaneously, with
there being no clear rules for who can modify what and the different
processes being typically delayed with respect to each other.
- avformat_find_stream_info() making it necessary to support opening
and closing a single codec context multiple times, thus
complicating the semantics of freeing various allocated objects in the
codec context.
Those problems are resolved by replacing the AVStream embedded codec
context with a newly added AVCodecParameters instance, which stores only
the stream parameters exported by the demuxers or read by the muxers.
Some .idx files actually contain duplicate subtitle events:
timestamp: 00:07:52:600, filepos: 00004e800
timestamp: 00:07:52:600, filepos: 00004f800
The second will be dropped, because it has same pts, duration, and text
(the text is just a dummy empty string; the real data is retrieved when
actually reading vobsub subtitle packets).
Dropping this is probably not intended/safe, so avoid it.
See trac issue #4872 for a sample. This patch doesn't fix decoding of
the sample, though.
The stream ID is essentially an arbitrary number defined by the .idx
file headers. They have to match the IDs in the .sub stream. The vobsub
demuxer assumed the IDs would just start from 0, increassing by 1 for
each stream. This is not correct. In the sample I had, the IDs were
starting from 1, leading to no subtitles being displayed at all.
Fix this by using the correct stream ID.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
If there is only 1 stream and seek isn't called with a specific stream
index, we pick the first (and only) one.
Regression since dbfe6110.
Fixes CID1108591.
Here is an extract of fate-samples/sub/vobsub.idx, with an additional
text at the end of each line to better identify each bitmap:
timestamp: 00:04:55:445, filepos: 00001b000 Ace!
timestamp: 00:05:00:049, filepos: 00001b800 Wake up, honey!
timestamp: 00:05:02:018, filepos: 00001c800 I gotta go to work.
timestamp: 00:05:02:035, filepos: 00001d000 <???>
timestamp: 00:05:04:203, filepos: 00001d800 Look after Clayton, okay?
timestamp: 00:05:05:947, filepos: 00001e800 I'll be back tonight.
timestamp: 00:05:07:957, filepos: 00001f800 Bye! Love you.
timestamp: 00:05:21:295, filepos: 000020800 Hey, Ace! What's up?
timestamp: 00:05:23:356, filepos: 000021800 Hey, how's it going?
timestamp: 00:05:24:640, filepos: 000022800 Remember what today is? The 3rd!
timestamp: 00:05:27:193, filepos: 000023800 Look over there!
timestamp: 00:05:28:369, filepos: 000024800 Where are they going?
timestamp: 00:05:28:361, filepos: 000025000 <???>
timestamp: 00:05:29:946, filepos: 000025800 Let's go see.
timestamp: 00:05:31:230, filepos: 000026000 I can't, man. I got Clayton.
Note the two "<???>": they are basically split subtitles (with the
previous one), which the dvdsub decoder is now supposed to reconstruct
with a previous commit. But also note that while the first chunk has
increasing timestamps,
timestamp: 00:05:02:018, filepos: 00001c800
timestamp: 00:05:02:035, filepos: 00001d000
...it's not the case of the second one (and this is not an exception in the
original file):
timestamp: 00:05:28:369, filepos: 000024800
timestamp: 00:05:28:361, filepos: 000025000
For the dvdsub decoder, they need to be "filepos'ed" ordered, but the
FFDemuxSubtitlesQueue is timestamps ordered, which is the reason of the
introduction of a sub sort method in the context, to allow giving
priority to the position, and then the timestamps. With that change, the
dvdsub decoder get fed with ordered packets.
Now the packet size estimation was also broken: the filepos differences
in the vobsub index defines the full data read between two subtitles
chunks, and it is necessary to take into account what is read by the
mpegps_read_pes_header() function since the length returned by that
function doesn't count the size of the data it reads. This is fixed with
the introduction of total_read, and {old,new}_pos. By doing this change,
we can drop the unreliable len16 heuristic and simplify the whole loop.
Note that mpegps_read_pes_header() often read more than one PES packet
(typically in one call it can read 0x1ba and 0x1be chunk along with the
relevant 0x1bd packet), which triggers the "total_read + pkt_size >
psize" check. This is an expected behaviour, which could be avoided by
having a more chunked version of mpegps_read_pes_header().
The latest change is the extraction of each stream into its own
subtitles queue. If we don't do this, the maximum size for a subtitle
chunk is broken, and the previous changes can not work. Having each
stream in a different queue requires some little adjustments in the
seek code of the demuxer.
This commit is only meaningful as a whole change and can not be easily
split. The FATE test changes because it uses the vobsub demuxer.
Remove the header decoding for PCM audio from mpeg.c and the
20/24bit parts from pcm.c and merge them into a new decoder in
pcm-dvd.c.
The decoder has added support for samples that span multiple
packets and modified 20/24bit group decoding. Both is needed to
decode samples that have been generated with DVD-Lab Pro 2. The
decoding of 16bit PCM and two channel 24bit is identical to
before. No other samples are known to verify the correctness of
the encoding this software does.
The complete list of tested formats is
48kHz/16bit/2-8 channels
48kHz/24bit/2-5 channels
96kHz/16bit/2-4 channels
96kHz/24bit/2 channels
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
