Hi,
On Mon, Nov 2, 2015 at 5:45 AM, Matthieu Bouron <matthieu.bou...@gmail.com>
wrote:
> From: Matthieu Bouron <matthieu.bou...@stupeflix.com>
>
> Avoid decoding a frame to get the codec parameters while the codec
> supports FF_CODEC_CAP_SKIP_FRAME_FILL_PARAM. This is particulary useful
> to avoid decoding twice images (once in avformat_find_stream_info and
> once when the actual decode is made).
> ---
> libavformat/utils.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/libavformat/utils.c b/libavformat/utils.c
> index 5c4d452..ba62f2b 100644
> --- a/libavformat/utils.c
> +++ b/libavformat/utils.c
> @@ -2695,6 +2695,8 @@ static int try_decode_frame(AVFormatContext *s,
> AVStream *st, AVPacket *avpkt,
> AVFrame *frame = av_frame_alloc();
> AVSubtitle subtitle;
> AVPacket pkt = *avpkt;
> + int do_skip_frame = 0;
> + enum AVDiscard skip_frame;
>
> if (!frame)
> return AVERROR(ENOMEM);
> @@ -2733,6 +2735,12 @@ static int try_decode_frame(AVFormatContext *s,
> AVStream *st, AVPacket *avpkt,
> goto fail;
> }
>
> + if (st->codec->codec->caps_internal &
> FF_CODEC_CAP_SKIP_FRAME_FILL_PARAM) {
> + do_skip_frame = 1;
> + skip_frame = st->codec->skip_frame;
> + st->codec->skip_frame = AVDISCARD_ALL;
> + }
> +
> while ((pkt.size > 0 || (!pkt.data && got_picture)) &&
> ret >= 0 &&
> (!has_codec_parameters(st, NULL) ||
> !has_decode_delay_been_guessed(st) ||
> @@ -2768,6 +2776,10 @@ static int try_decode_frame(AVFormatContext *s,
> AVStream *st, AVPacket *avpkt,
> ret = -1;
>
> fail:
> + if (do_skip_frame) {
> + st->codec->skip_frame = skip_frame;
> + }
> +
> av_frame_free(&frame);
> return ret;
> }
> --
> 2.6.2
I think we need an assert in the try_decode loop to ensure that it indeed
did fill all the params. This is to prevent the case where someone adds a
new "thing" to the list of things required for find_stream_info to succeed,
and forgets to update the codecs.
(These features break easily and subtly, and ideally we'd detect such
breakage in fate, not 6 months after the next release.)
Ronald
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