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

[Lukasz Marek]

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.