[FFmpeg-devel] [PATCH] mmaldec: Set the output pix_fmt after detecting format

[Julian Scheel]

Am 21.10.2015 um 16:18 schrieb wm4:
> On Wed, 21 Oct 2015 16:07:08 +0200
> Hendrik Leppkes <h.leppkes at gmail.com> wrote:
>
>> On Wed, Oct 21, 2015 at 3:55 PM, Julian Scheel <julian at jusst.de> wrote:
>>> Wait for the first decoded frame to be returned by mmal before setting
>>> pix_fmt. This is important for avformat probing to work properly as it is one
>>> of the criterions to decide whether to decode a frame or not for probing.
>>>
>>> Signed-off-by: Julian Scheel <julian at jusst.de>
>>> ---
>>>   libavcodec/mmaldec.c | 10 +++++-----
>>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/libavcodec/mmaldec.c b/libavcodec/mmaldec.c
>>> index 7db90d2..429990a 100644
>>> --- a/libavcodec/mmaldec.c
>>> +++ b/libavcodec/mmaldec.c
>>> @@ -338,11 +338,6 @@ static av_cold int ffmmal_init_decoder(AVCodecContext *avctx)
>>>           return AVERROR(ENOSYS);
>>>       }
>>>
>>> -    if ((ret = ff_get_format(avctx, avctx->codec->pix_fmts)) < 0)
>>> -        return ret;
>>> -
>>> -    avctx->pix_fmt = ret;
>>> -
>>>       if ((status = mmal_component_create(MMAL_COMPONENT_DEFAULT_VIDEO_DECODER, &ctx->decoder)))
>>>           goto fail;
>>>
>>> @@ -678,6 +673,11 @@ static int ffmmal_read_frame(AVCodecContext *avctx, AVFrame *frame, int *got_fra
>>>
>>>               av_log(avctx, AV_LOG_INFO, "Changing output format.\n");
>>>
>>> +            if ((ret = ff_get_format(avctx, avctx->codec->pix_fmts)) < 0)
>>> +                return ret;
>>> +
>>> +            avctx->pix_fmt = ret;
>>> +
>>>               if ((status = mmal_port_disable(decoder->output[0])))
>>>                   goto done;
>>>
>>
>> pix_fmt is already used by the decoder before this point to decide if
>> mmal surfaces or memory buffers are to be used, changing it afterwards
>> will not have the same effect as doing it in init.
>
> Oh, you're right. It's used in ffmal_update_format(), so this patch can
> only work if the decoder sends MMAL_EVENT_FORMAT_CHANGED on init, or if
> the entire decoding init is delayed and not done in AVCodec.init.

I think it would be sufficient to query the pix_fmt via ff_get_format in 
ffmal_update_format instead of using avctx->pix_fmt. The other paramters 
should be changeable without disabling the port. But this should be 
tested probably :)
Regarding the question if MMAL_EVENT_FORMAT_CHANGED will be sent by the 
decoder in any case I have opened an issue for clarification: 
https://github.com/raspberrypi/firmware/issues/489

-Julian