[FFmpeg-devel] [PATCH 04/11] avformat/muxers: Add non-blocking mode support for av_write_trailer

[Jan Sebechlebsky]

On 08/10/2016 07:04 PM, Michael Niedermayer wrote:

> On Tue, Aug 02, 2016 at 03:24:15PM +0200, sebechlebskyjan at gmail.com wrote:
>> From: Jan Sebechlebsky <sebechlebskyjan at gmail.com>
>>
>> This makes av_write_trailer not to free the resources if write_trailer
>> call returns AVERROR(EAGAIN) allowing repeated calls of write_trailer of
>> non-blocking muxer.
>>
>> Signed-off-by: Jan Sebechlebsky <sebechlebskyjan at gmail.com>
>> ---
>>   libavformat/avformat.h | 6 +++++-
>>   libavformat/mux.c      | 3 +++
>>   2 files changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
>> index 818184e..9191c69 100644
>> --- a/libavformat/avformat.h
>> +++ b/libavformat/avformat.h
>> @@ -2508,8 +2508,12 @@ int av_write_uncoded_frame_query(AVFormatContext *s, int stream_index);
>>    *
>>    * May only be called after a successful call to avformat_write_header.
>>    *
>> + * If AVFMT_FLAG_NONBLOCK is set, this call may return AVERROR(EAGAIN)
>> + * meaning the operation is pending and the call should be repeated.
>> + *
>>    * @param s media file handle
>> - * @return 0 if OK, AVERROR_xxx on error
>> + * @return 0 if OK, AVERROR(EAGAIN) in case call should be repeated,
>> + *         other AVERROR on error
>>    */
>>   int av_write_trailer(AVFormatContext *s);
>>   
>> diff --git a/libavformat/mux.c b/libavformat/mux.c
>> index e9973ed..b58e4c1 100644
>> --- a/libavformat/mux.c
>> +++ b/libavformat/mux.c
>> @@ -1238,6 +1238,9 @@ fail:
>>           }
>>       }
>>   
>> +    if (ret == AVERROR(EAGAIN))
>> +        return ret;
> IIUC the non blocking code works only if packet interleaving is not
> used (which is implied by AVFMT_FLAG_NONBLOCK being set)
>
> is there an assert ensuring that EAGAIN only occurs in such case
> somewhere ?
I've just added comment to av_interleaved_write_frame that it cannot be 
used with muxer
operating in non-blocking mode, but it is certainly good idea to add 
assert as well.
I'll modify and resend the patch with the comment change to add assert too.

> if it would occur with the interleave code then
> ret could be set before or maybe even set to EAGAIN and then
>
>      if (s->internal->header_written && s->oformat->write_trailer) {
>          if (!(s->oformat->flags & AVFMT_NOFILE) && s->pb)
>              avio_write_marker(s->pb, AV_NOPTS_VALUE, AVIO_DATA_MARKER_TRAILER);
>          if (ret >= 0) {
>          ret = s->oformat->write_trailer(s);
>          } else {
>              s->oformat->write_trailer(s);
>          }
>      }
>
> would do all kinds of unexpected things like ignoring the write_trailer
> return  or returning to the user EAGAIN even when trailer didnt return
> that, ...
>
> [...]
>
>
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Regards,
Jan