[FFmpeg-devel] [PATCH 2/2] ffmpeg: use avcodec_copy_context before avcodec_open2 and open both ctxs

Michael Niedermayer michaelni at gmx.at
Wed Dec 3 03:15:27 CET 2014


On Wed, Dec 03, 2014 at 02:02:21AM +0100, Lukasz Marek wrote:
> On 03.12.2014 01:53, Michael Niedermayer wrote:
> >On Wed, Dec 03, 2014 at 01:39:12AM +0100, Lukasz Marek wrote:
> >>On 03.12.2014 00:35, Michael Niedermayer wrote:
> >>>On Tue, Dec 02, 2014 at 07:27:33PM +0100, Lukasz Marek wrote:
> >>>>avcodec_copy_context make dest context unopened.
> >>>>ffmpeg treats it as opened.
> >>>>
> >>>>Signed-off-by: Lukasz Marek <lukasz.m.luki2 at gmail.com>
> >>>>---
> >>>>  ffmpeg.c | 29 ++++++++++++++++++++---------
> >>>>  1 file changed, 20 insertions(+), 9 deletions(-)
> >>>>
> >>>>diff --git a/ffmpeg.c b/ffmpeg.c
> >>>>index b44401f..4fa9f1e 100644
> >>>>--- a/ffmpeg.c
> >>>>+++ b/ffmpeg.c
> >>>>@@ -2932,6 +2932,7 @@ static int transcode_init(void)
> >>>>          if (ost->encoding_needed) {
> >>>>              AVCodec      *codec = ost->enc;
> >>>>              AVCodecContext *dec = NULL;
> >>>>+            AVDictionary   *opt_copy = NULL;
> >>>>
> >>>>              if ((ist = get_input_stream(ost)))
> >>>>                  dec = ist->dec_ctx;
> >>>>@@ -2949,13 +2950,24 @@ static int transcode_init(void)
> >>>>                  av_dict_set(&ost->encoder_opts, "threads", "auto", 0);
> >>>>              av_dict_set(&ost->encoder_opts, "side_data_only_packets", "1", 0);
> >>>>
> >>>>-            if ((ret = avcodec_open2(ost->enc_ctx, codec, &ost->encoder_opts)) < 0) {
> >>>>+            ret = avcodec_copy_context(ost->st->codec, ost->enc_ctx);
> >>>>+            if (ret < 0) {
> >>>>+                av_log(NULL, AV_LOG_FATAL,
> >>>>+                       "Error initializing the output stream codec context.\n");
> >>>>+                exit_program(1);
> >>>>+            }
> >>>>+
> >>>>+            av_dict_copy(&opt_copy, ost->encoder_opts, 0);
> >>>>+            if ((ret = avcodec_open2(ost->enc_ctx, codec, &ost->encoder_opts)) < 0 ||
> >>>>+                (ret = avcodec_open2(ost->st->codec, codec, &opt_copy)) < 0) {
> >>>
> >>>if the encoder is opened twice it would print any info or warnings
> >>>twice. libxvid would open 2pass files twice potentially i think
> >>>
> >>>maybe coded_frame could just be allocated somewhere before use
> >>>in ffmpeg raw and leaving the copy as it is in ffmpeg ?
> >>
> >>I'm not familiar with ffmpeg.c code closely; is ost->st->codec
> >>context used by ffmpeg for anything? I guess not (but im not sure).
> >>If so, I think is all working because of that. You have two contexts
> >>that share some pointers (like mentioned coded_frame). Of cource it
> >>can be reallocated here, but this code is still in contradiction
> >>with doxy of avcodec_copy_context that states dest context should be
> >>treat as  not opened. FFmpeg uses it as opened.
> >
> >where does ffmpeg treat the context as open ?
> 
> I saw this coded_frame allocated in init function of codecs, so I
> assumed that.
> 
> >i know of the coded_frame case but thats only used to transfer some
> >flags into the muxer and isnt really a pretty way to do it but
> >for that simply allocating the frame so the flags can be set
> >should work
> >i mean you can probably just check if its NULL and allocate
> >before the few flags are set in it
> 
> So basically, I can just alloc it in avcodec_copy_context in case it
> is present in src object? It is working, but I thought it is wrong
> way to solve it.

I suspect that would lead to some memleak, also it doesnt feel
right.
Ive removed the troubblesome coded_frame use in ffmpeg.c, it served
no purpose anymore
does that solve the issue?

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Into a blind darkness they enter who follow after the Ignorance,
they as if into a greater darkness enter who devote themselves
to the Knowledge alone. -- Isha Upanishad
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