[FFmpeg-devel] [PATCH v2 04/11] avformat/muxers: Add non-blocking mode support for av_write_trailer

[Jan Sebechlebsky]

On 08/22/2016 04:49 PM, Michael Niedermayer wrote:

> On Mon, Aug 22, 2016 at 04:27:16PM +0200, Jan Sebechlebsky wrote:
>>
>> On 08/22/2016 09:51 AM, Michael Niedermayer wrote:
>>> On Thu, Aug 11, 2016 at 02:38:29PM +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>
>>>> ---
>>>>   Changes since the last version of the patch:
>>>>   - Added assert to the part of the code dealing with flushing
>>>>     interleaved packets which should not be entered if
>>>>     muxer in non-blocking mode is used.
>>>>     (also there is assert for the same condition added into
>>>>      av_interleaved_write_packet in one of the following
>>>>      patches).
>>>>
>>>>   libavformat/avformat.h |  6 +++++-
>>>>   libavformat/mux.c      | 10 ++++++++--
>>>>   2 files changed, 13 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
>>>> index d8a6cf3..2cc3156 100644
>>>> --- a/libavformat/avformat.h
>>>> +++ b/libavformat/avformat.h
>>>> @@ -2510,8 +2510,12 @@ 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..3ae924c 100644
>>>> --- a/libavformat/mux.c
>>>> +++ b/libavformat/mux.c
>>>> @@ -1204,11 +1204,14 @@ int av_write_trailer(AVFormatContext *s)
>>>>       for (;; ) {
>>>>           AVPacket pkt;
>>>>           ret = interleave_packet(s, &pkt, NULL, 1);
>>>> -        if (ret < 0)
>>>> -            goto fail;
>>>>           if (!ret)
>>>>               break;
>>>> +        av_assert0(!(s->flags & AVFMT_FLAG_NONBLOCK));
>>> this would abort on any error not just EAGAIN
>> I think it will abort in case interleave_packets does not return 0
>> from the first call in loop, which means that interleaving was used
>> (because there are some packets to be flushed) and that situation
>> cannot happen with AVFMT_FLAG_NONBLOCK set when interleaving is
>> forbidded. The next patch also adds assert to
>> av_interleaved_write_packet. But I think the assert here is on the
>> right place, or have I misunderstood the problem you're pointing
>> out?
> I thought interleave_packet can return AVERROR(ENOMEM)
> maybe this is not possible, still it seems non-robust to assert if
> it errors out
>
I think it cannot return AVERROR(ENOMEM) in case interleaving was not 
used. But maybe I can remove assert from this function since there will 
be assert in av_interleaved_write_frame?

Regards,
Jan