Statistics
| Branch: | Revision:

ffmpeg / ffmpeg.c @ master

History | View | Annotate | Download (167 KB)

# Date Author Comment
a4b6000b 05/17/2011 02:57 PM Michael Niedermayer

ffmpeg: reset top_field_first in opt_input_file().

This allows seting tff for inputs without also setting it for the output
Signed-off-by: Michael Niedermayer <>

f8ae3a21 05/17/2011 02:51 AM Michael Niedermayer

Merge remote branch 'qatar/master'

12 files changed, 36 insertions(+), 81 deletions(-)
yes thats 36 new lines in 14 commits

  • qatar/master:
    ffmpeg: fix -aspect cli option
    Restructure video filter implementation in ffmpeg.c.
    ffplay: remove audio_write_get_buf_size() forward declaration...
901ff511 05/16/2011 09:13 PM Baptiste Coudurier

ffmpeg: fix -aspect cli option

Redesign the way -aspect option is handled. This is done by making
ffmpeg read the sample aspect ratio set in the corresponding input
stream by default, and overriding it using the value specified by
-aspect.

If the output display aspect ratio is specified with -aspect, it is...

9d5fa618 05/16/2011 09:13 PM Michael Niedermayer

Restructure video filter implementation in ffmpeg.c.

This fixes several bugs like multiple outputs and -aspect mixed with -vf

(cherry picked from commit 1762d9ced70ccc46c5d3e5d64e56a48d0fbbd4f7)
(cherry picked from commit 5c20c81bfa526b3a269db9c88b0c9007861f0917)...

9763420b 05/16/2011 07:52 PM Michael Niedermayer

rawdec: Allow overriding top field first.

Iam not sure this is the best way to implement it, but its the simplest
and keeps the code seperate from the application. Keeping ffmpeg.c
simple and not requireing user apps to duplicate this code.
Signed-off-by: Michael Niedermayer <>

19878374 05/16/2011 07:26 PM Michael Niedermayer

ffmpeg: initialize input_codec array earlier.

Signed-off-by: Michael Niedermayer <>

90bb2c78 05/14/2011 11:39 PM Michael Niedermayer

ffmpeg: Allow seting and cycling through debug modes.

Signed-off-by: Michael Niedermayer <>

34e83808 05/14/2011 01:52 PM Michael Niedermayer

ffmpeg: Help for interactive keys.

Signed-off-by: Michael Niedermayer <>

0f6a8579 05/14/2011 12:54 AM Michael Niedermayer

ffmpeg: Interactivity support. Try pressing +-hs.

Signed-off-by: Michael Niedermayer <>

dbe94539 05/13/2011 05:38 AM Stefano Sabatini

ffmpeg: use parse_number_and_die() when it makes sense

Prefer parse_number_or_die() over atoi()/atol() parsing for the options:
-pass, -top, -vc, and -qscale.

Improve input validation.

Signed-off-by: Stefano Sabatini <>
Signed-off-by: Anton Khirnov <>

8fb566fd 05/13/2011 05:38 AM Anton Khirnov

ffmpeg: get rid of the 'q' key schizofrenia

SIGINT for quitting should be enough for everybody.

72153419 05/13/2011 02:40 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master: (33 commits)
    rtpdec_qdm2: Don't try to parse data packet if no configuration is received
    ac3enc: put the counting of stereo rematrixing bits in the same place to make the code easier to understand.
    ac3enc: clean up count_frame_bits() and count_frame_bits_fixed()...
5da116a3 05/12/2011 04:02 PM Michael Niedermayer

ffmpeg: factorize quality calculation

Calculate quality value once per stream in print_report().
Also fix segfault, as coded_frame can be NULL.

Signed-off-by: Anton Khirnov <>

046f081b 05/12/2011 09:41 AM Diego Biurrun

configure: Do not unconditionally add -D_POSIX_C_SOURCE to CPPFLAGS.

Adding _POSIX_C_SOURCE to CPPFLAGS globally produces all sorts of problems
since it causes certain system functions to be hidden on some (BSD) systems.
The solution is to only add the flag on systems that really require it, i.e....

612122b1 05/12/2011 02:51 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master: (32 commits)
    10-bit H.264 x86 chroma v loopfilter asm
    Port SMPTE S302M audio decoder from FFmbc 0.3. [Copyright headers corrected]
    Fix crash of interlaced MPEG2 decoding
    h264pred: fix one more aliasing violation....
3fd62c6e 05/11/2011 05:32 AM Stefano Sabatini

ffmpeg: call pre_process_video_frame() only if decoding is needed

In output_packet(), move the pre_process_video_frame() call inside the
if (ist->decoding_needed) { } block. This way
pre_process_video_frame() is not called when stream-copy has been
selected....

2b95602e 05/11/2011 05:32 AM Stefano Sabatini

ffmpeg: reformat resample condition code in transcode()

Signed-off-by: Stefano Sabatini <>
Signed-off-by: Anton Khirnov <>

9aa797cd 05/11/2011 05:32 AM Stefano Sabatini

ffmpeg: factorize resampling condition check in do_video_out()

Simplify and improve readability.

Signed-off-by: Stefano Sabatini <>
Signed-off-by: Anton Khirnov <>

c29c2eea 05/11/2011 05:32 AM Stefano Sabatini

ffmpeg: prefer "dec" over "ist->st->codec" in do_video_out() snippet

Simplify, ease readability.

Signed-off-by: Stefano Sabatini <>
Signed-off-by: Anton Khirnov <>

2ecc5b70 05/11/2011 05:32 AM Stefano Sabatini

ffmpeg: improve reporting if size/pixel format changes

Use av_log() rather than fprintf(stderr, ...), and show information
related to the previous size/pixel format configuration.

Consistent with the corresponding message issued in case of audio
configuration change....

b568d6d9 05/11/2011 05:32 AM Stefano Sabatini

ffmpeg: warns the user when the selected pixel format is ignored

Signed-off-by: Anton Khirnov <>

59eb12fa 05/11/2011 03:47 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master: (30 commits)
    AVOptions: make default_val a union, as proposed in AVOption2.
    arm/h264pred: add missing argument type.
    h264dsp_mmx: place bracket outside #if/#endif block.
    lavf/utils: fix ff_interleave_compare_dts corner case....
b5e08992 05/10/2011 10:57 PM Robert Leatherwood

"Initialize" copy_tb like the other global variables.

eeaba924 05/10/2011 03:31 PM Michael Niedermayer

ffmpeg: Fix -t with files that do not have any timestamps.

This for example fixes -t with some frext h264 reference streams.
Signed-off-by: Michael Niedermayer <>

cb48fdf6 05/10/2011 11:23 AM Alexander Strange

ffmpeg: Simplify decode loop condition to not use next_pts

Signed-off-by: Ronald S. Bultje <>

bc97695a 05/10/2011 05:17 AM Stefano Sabatini

ffmpeg: remove unused fields AVOutputStream.original_width/height

Signed-off-by: Stefano Sabatini <>
Signed-off-by: Anton Khirnov <>

f38d900f 05/10/2011 05:17 AM Stefano Sabatini

ffmpeg: remove unused variable padding_src in do_video_out()

Signed-off-by: Stefano Sabatini <>
Signed-off-by: Anton Khirnov <>

d1991f51 05/10/2011 05:17 AM Michael Niedermayer

ffmpeg: fix negative verbosity.

Signed-off-by: Anton Khirnov <>

0420bf09 05/10/2011 05:15 AM Stefano Sabatini

ffmpeg: rename configure_filters() to configure_video_filters()

Mostly useful for the audio-filters branch, to make more apparent the
distinction between configure_audio_filters() and
configure_video_filters().

Signed-off-by: Stefano Sabatini <>...

5d2c6f42 05/10/2011 05:14 AM Stefano Sabatini

cmdutils: remove list_fmts(), simplify

The function was only used in opt_sample_fmt() for listing the sample
formats. Move list_fmts() functionality directly into
opt_sample_fmt().

Also fix the warning:
ffmpeg.c: In function ‘opt_audio_sample_fmt’:
ffmpeg.c:2877: warning: passing argument 1 of ‘list_fmts’ from incompatible pointer type...

c3e40410 05/10/2011 05:12 AM Takashi Mochizuki

Add missing CONFIG_AVFILTER check.

Fix configure --disable-avfilter issue.

Signed-off-by: Anton Khirnov <>

b97b4b58 05/10/2011 02:03 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master:
    mpegaudiodec: group #includes more sanely
    mpegaudio: remove #if 0 blocks
    ffmpeg.c: reset avoptions after each input/output file.
    ffmpeg.c: store per-output stream sws flags.
    mpegaudio: remove CONFIG_MPEGAUDIO_HP option...
19615089 05/09/2011 05:35 PM Anton Khirnov

ffmpeg.c: reset avoptions after each input/output file.

This is consistent with how all the other options work.

1435f2fa 05/09/2011 05:35 PM Anton Khirnov

ffmpeg.c: store per-output stream sws flags.

6841c8c5 05/09/2011 02:50 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master:
    log: Fix an oob array read.
    cosmetics: trim trailing whitespace in postproc
    Ban strncpy() it's too easy to misuse.
    psymodel: Remove wrapper functions.
    aacenc: Replace loop counters in aac_encode_frame() with more descriptive 'ch' and 'w'....
648e55ff 05/08/2011 08:43 AM Anton Khirnov

ffmpeg.c: check for interlaced flag in the correct place.

In the corresponding codec context, not global options storage.

64c06615 05/07/2011 10:03 AM Stefano Sabatini

vsrc_buffer: simplify av_vsrc_buffer_add_frame*() interface

Now that pix_fmt, width, and height are directly embedded in the AVFrame,
there is no need to pass these values as separate arguments.

2beac7c3 05/07/2011 10:03 AM Stefano Sabatini

ffmpeg: rename ost->pict_tmp to ost->resample_frame

The new name is more consistent with the employed naming scheme, and
more meaningful.

04c373c1 05/07/2011 10:03 AM Stefano Sabatini

ffmpeg: prefer dec/enc over ost/ist->st->codec in do_video_out()

Compact code, improve readability.

a851fa7f 05/07/2011 10:03 AM Stefano Sabatini

ffmpeg: move resample_changed check within the #if !CONFIG_AVFILTER

The check and the corresponding message in do_video_out() are
unnecessary in the libavfilter path, as a similar check and message
are performed within the buffer source.

70c24b21 05/07/2011 10:03 AM Stefano Sabatini

ffmpeg: remove useless intermediary variable resample_dst in do_video_out()

f5a669c2 05/07/2011 10:03 AM Stefano Sabatini

ffmpeg: simplify mid-stream reconfiguration when libavfilter is disabled

Implement lazy initialization of the image resample context, so that
the initialization code does not need to be duplicated.

Also manage the case in which resample/size change mid-stream. For...

566666ca 05/07/2011 10:03 AM Stefano Sabatini

lavfi: add libavfilter/avcodec.h and avfilter_copy_frame_props()

avfilter_copy_frame_props() avoids code duplication and increases
robustness.

The added files libavfilter/avcodec.[ch] are used for containing
utilities useful for gluing togheter libavfilter and libavcodec.

b000b86e 05/05/2011 01:30 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master: (23 commits)
    doc: Check standalone compilation before submitting new components.
    Fix standalone compilation of pipe protocol.
    Fix standalone compilation of ac3_fixed encoder.
    Fix standalone compilation of binkaudio_dct / binkaudio_rdft decoders....
1a5e4fd8 05/04/2011 04:20 AM Alex Converse

Replace strncpy() with av_strlcpy().

707e8612 05/04/2011 02:06 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master:
    Implement fate-rsync target
    Make ffmpeg support generic data stream

Conflicts:
cmdutils.h

Merged-by: Michael Niedermayer <>

e3b540b4 05/03/2011 09:51 AM Luca Barbato

Make ffmpeg support generic data stream

The patch is the first step to support -dcodec copy

2525821f 05/03/2011 02:08 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master:
    vp8: frame-multithreading.
    Duplicate Replace deprecated FF_*_TYPE symbols with AV_PICTURE_TYPE_*.
    Duplicate Replace deprecated av_get_pict_type_char() with av_get_picture_type_char().
    Bug spoted&removed in last merge: dpx: Do not use DPX encoder for decoding....
ce5e49b0 05/02/2011 02:41 PM Stefano Sabatini

replace deprecated FF_*_TYPE symbols with AV_PICTURE_TYPE_*

301183d9 05/02/2011 02:41 PM Stefano Sabatini

replace deprecated av_get_pict_type_char() with av_get_picture_type_char()

975a1447 05/02/2011 10:18 AM Stefano Sabatini

Replace deprecated FF_*_TYPE symbols with AV_PICTURE_TYPE_*.

Signed-off-by: Diego Biurrun <>

6209669d 05/02/2011 09:24 AM Stefano Sabatini

Replace deprecated av_get_pict_type_char() with av_get_picture_type_char().

Signed-off-by: Diego Biurrun <>

35fe66ab 05/01/2011 11:10 AM Stefano Sabatini

lavfi: rename AVFilterBufferRefVideoProps.pixel_aspect to sample_aspect_ratio

Improve consistency with libavcodec.

This breaks libavfilter API/ABI.

The non-sequential 2.1.0 -> 2.4.0 bump is due to the mess previously
done with the lavfi minor number.

77e9dee8 05/01/2011 11:10 AM Stefano Sabatini

lavc: add a sample_aspect_ratio field to AVFrame

The sample aspect ratio is a per-frame property, so it makes sense to
define it in AVFrame rather than in the codec/stream context.
Simplify application-level sample aspect ratio information extraction,
and allow further simplifications.

fa119522 04/30/2011 08:09 PM Michael Niedermayer

FFMPEG: support demuxer specific options.
Signed-off-by: Michael Niedermayer <>

7d727f13 04/30/2011 08:09 PM Michael Niedermayer

LAVFAPI: avformat_alloc_output_context() / simplify usage of muxers.
Signed-off-by: Michael Niedermayer <>

be315a32 04/29/2011 11:58 PM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master:
    Duplicate AMV: disable DR1 and don't override EMU_EDGE
    Duplicate lavf: inspect more frames for fps when container time base is coarse
    Wrong and we have correct fix: Fix races in default av_log handler
    vorbis: Replace sized int_fast integer types with plain int/unsigned....
2e15305b 04/29/2011 06:00 PM Diego Biurrun

Remove some disabled printf debug cruft.

0886267e 04/27/2011 12:09 PM Michael Niedermayer

Revert buggy hunk that leaked in from a libav merge.
This unbreaks compilation with --disable-avfilter.
Signed-off-by: Michael Niedermayer <>

d7e5aeba 04/27/2011 01:51 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master: (23 commits)
    ac3enc: correct the flipped sign in the ac3_fixed encoder
    Eliminate pointless '#if 1' statements without matching '#else'.
    Add AVX FFT implementation.
    Increase alignment of av_malloc() as needed by AVX ASM....
a38cdfde 04/26/2011 04:16 PM Michael Niedermayer

vsrc_buffer: Set output size
Signed-off-by: Michael Niedermayer <>

7a11c82f 04/26/2011 05:38 AM Michael Niedermayer

vsrc_buffer: add sample_aspect_ratio fields to arguments.

This fixes aspect handling in ffmpeg.

This is based on a patch by Baptiste.

Signed-off-by: Anton Khirnov <>

7b376b39 04/24/2011 01:41 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master:
    Handle unicode file names on windows
    rtp: Rename the open/close functions to alloc/free
    Lowercase all ff* program names.
    Refer to ff* tools by their lowercase names.
    NOT Pulled Replace more FFmpeg instances by Libav or ffmpeg....
89b503b5 04/23/2011 05:12 PM Diego Biurrun

Lowercase all ff* program names.

3c483620 04/22/2011 04:49 PM Carl Eugen Hoyos

Cosmetics: Rename variable daemon as run_as_daemon.

daemon() is defined in unistd.h for BSD and Cygwin.

8772156b 04/22/2011 01:54 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master:
    APIChanges: document git revision for CODEC_CAP_SLICE_THREADS addition.
    Introduce slice threads flag.
    FATE: allow forcing thread-type when doing threaded fate runs.
    Use av_log_ask_for_sample() where appropriate....
7046b63e 04/21/2011 10:08 AM Stefano Sabatini

ffmpeg: call pre_process_video_frame() only if decoding is needed

In output_packet(), move the pre_process_video_frame() call inside the
if (ist->decoding_needed) { } block. This way
pre_process_video_frame() is not called when stream-copy has been
selected....

79157f40 04/21/2011 05:10 AM Stefano Sabatini

error: remove AVERROR_NUMEXPECTED

AVERROR_NUMEXPECTED is used only in the image muxer and demuxer, and
has a too much specific meaning, which is better explained through a
log message. Thus it can be replaced by AVERROR.

This breaks API.

Signed-off-by: Stefano Sabatini <>...

2c18893a 04/20/2011 10:46 PM Baptiste Coudurier

In libx264 wrapper, correctly support 2pass log filename option.

efb5fa79 04/20/2011 02:48 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master: (37 commits)
    In avcodec_open(), set return code to an error value only when an error occurs instead of unconditionally at the start of the function.
    lavc: remove reference to opt.h from Makefile.
    prefer avio_check() over url_exist()...
55815edc 04/19/2011 05:48 PM Stefano Sabatini

prefer avio_check() over url_exist()

The problem with url_exist() is that it tries to open a resource in
RDONLY mode. If the file is a FIFO and there is already a reading
client, the open() call will hang.

By using avio_check() with access mode of 0, the second reading...

59d96941 04/19/2011 05:47 PM Stefano Sabatini

avio: remove AVIO_* access symbols in favor of new AVIO_FLAG_* symbols

Make AVIO_FLAG_ access constants work as flags, and in particular fix
the behavior of functions (such as avio_check()) which expect them to
be flags rather than modes.

This breaks API.

41d0eb1c 04/19/2011 04:41 PM Anton Khirnov

lavc: remove the FF_API_SET_STRING_OLD cruft.

761ad429 04/19/2011 04:28 PM Anton Khirnov

lavf: remove FF_API_MAX_STREAMS cruft

c438c907 04/19/2011 10:23 AM Stefano Sabatini

ffmpeg: reformat resample condition code in transcode()

Signed-off-by: Stefano Sabatini <>

0f230c53 04/19/2011 10:23 AM Stefano Sabatini

ffmpeg: factorize resampling condition check in do_video_out()

Simplify and improve readability.

Signed-off-by: Stefano Sabatini <>

6a46aab4 04/19/2011 10:23 AM Stefano Sabatini

ffmpeg: prefer "dec" over "ist->st->codec" in do_video_out() snippet

Simplify, ease readability.

Signed-off-by: Stefano Sabatini <>

dfc6f5ae 04/19/2011 10:23 AM Stefano Sabatini

ffmpeg: improve reporting if size/pixel format changes

Use av_log() rather than fprintf(stderr, ...), and show information
related to the previous size/pixel format configuration.

Consistent with the corresponding message issued in case of audio
configuration change....

58bc9ac5 04/19/2011 10:23 AM Stefano Sabatini

ffmpeg: remove unused fields AVOutputStream.original_width/height

Signed-off-by: Stefano Sabatini <>

b0b83973 04/19/2011 10:23 AM Stefano Sabatini

ffmpeg: remove unused variable padding_src in do_video_out()

Signed-off-by: Stefano Sabatini <>

39aafa5e 04/18/2011 11:54 PM Michael Niedermayer

ffmpeg:Daemon mode, add -d as first option to try it.
Signed-off-by: Michael Niedermayer <>

17ee7b55 04/18/2011 11:54 PM Michael Niedermayer

ffmpeg:Fix negative verbositiy
Signed-off-by: Michael Niedermayer <>

abf8342a 04/16/2011 11:47 PM Baptiste Coudurier

ffmpeg: fix -aspect cli option

Redesign the way -aspect option is handled. This is done by making
ffmpeg read the sample aspect ratio set in the corresponding input
stream by default, and overriding it using the value specified by
-aspect.

If the output display aspect ratio is specified with -aspect, it is...

bdf3d3bf 04/16/2011 07:47 PM Stefano Sabatini

ffmpeg: use parse_number_and_die() when it makes sense

Prefer parse_number_or_die() over atoi()/atol() parsing for the options:
-pass, -top, -vc, and -qscale.

Improve input validation.

Signed-off-by: Stefano Sabatini <>

5381823e 04/10/2011 10:14 PM Stefano Sabatini

ffmpeg: rename configure_filters() to configure_video_filters()

Mostly useful for the audio-filters branch, to make more apparent the
distinction between configure_audio_filters() and
configure_video_filters().

Signed-off-by: Stefano Sabatini <>

f8de11cf 04/10/2011 07:27 AM Lou Logan

Redefine sameq

I think the documentation of sameq is causing confusion and misuse of
this option.

Signed-off-by: Michael Niedermayer <>
Signed-off-by: Anton Khirnov <>

d4d09329 04/09/2011 01:17 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master:
    lavf: bump minor and add an APIChanges entry for avformat cleanup
    lavf: get rid of ffm-specific stuff in avformat.h
    Not pulled: avio: deprecate av_protocol_next().
    avio: add a function for iterating though protocol names....
3ee53dab 04/08/2011 06:58 PM Anton Khirnov

lavf: get rid of ffm-specific stuff in avformat.h

c3675dfe 04/08/2011 02:45 PM Anton Khirnov

lavf: rename avf_sdp_create to av_sdp_create.

The new name is more consistent with the rest of the API.

c88caa52 04/08/2011 12:50 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master:
    proto: include os_support.h in network.h
    matroskaenc: don't write an empty Cues element.
    lavc: add a FF_API_REQUEST_CHANNELS deprecation macro
    avio: move extern url_interrupt_cb declaration from avio.h to url.h...
80c6e238 04/07/2011 04:11 PM Anton Khirnov

avio: avio_ prefix for url_set_interrupt_cb.

f87b1b37 04/07/2011 04:07 PM Anton Khirnov

avio: AVIO_ prefixes for URL_ open flags.

6b1c886b 04/06/2011 09:21 PM Michael Niedermayer

Fix ticket20
Signed-off-by: Michael Niedermayer <>

d6c85865 04/06/2011 01:01 AM Michael Niedermayer

Revert "ffmpeg: fix aspect ratio setting"

This reverts commit d1eb50bb29caad9745631759265f475177df99b9.
Reason, it breaks fate

11d78415 04/06/2011 12:59 AM Michael Niedermayer

Merge remote branch 'qatar/master'

  • qatar/master:
    psymodel: extend API to include PE and bit allocation.
    avio: always compile dyn_buf functions
    Remove unnecessary parameter from ff_thread_init() and fix behavior
    Revert "aac_latm_dec: use aac context and aac m4ac"...
b5ef6f8e 04/05/2011 11:09 PM Michael Niedermayer

Fix crash in ffmpeg.c with PIX_FMT_NONE
Signed-off-by: Michael Niedermayer <>

d1eb50bb 04/05/2011 01:33 PM Stefano Sabatini

ffmpeg: fix aspect ratio setting

This is done by adding a setsar filter at the beginning of the
configured filterchain.

This implementation is more robust, since does not modify the
filterchain description (which was creating potential syntax errors),
but directly modifies the filterchain structure....

14cf0fd2 04/05/2011 07:08 AM Alex Converse

Add silence support for AV_SAMPLE_FMT_U8.

Signed-off-by: Anton Khirnov <>

8af3167b 04/05/2011 01:21 AM Lou Logan

Redefine sameq

I think the documentation of sameq is causing confusion and misuse of
this option.

Signed-off-by: Michael Niedermayer <>

100a6b7c 04/03/2011 10:35 PM Peter Ross

ffmpeg: make 'bits_per_raw_sample' option more useful

Currently bits_per_raw_sample is exposed as an AVCodecContext option.
The option is not very useful, because ffmpeg 1) overwrites it with
a value from the upstream codec, or 2) it resets the value whenever...