[FFmpeg-devel] [PATCH] libavcodec/h261dec: Fix keyframe markup and frame skipping.

[Carl Eugen Hoyos]

Am Sa., 26. Okt. 2019 um 13:12 Uhr schrieb Andrey Semashev
<andrey.semashev at gmail.com>:
>
> The decoder never marks pictures as I-frames, which results in no
> keyframe indication and incorrect frame skipping, in cases when
> keyframes should be decoded.
>
> This commit works around this decoder limitation and marks I-frames
> and keyframes based on "freeze picture release" bit in h261 picture
> header. This reflects h261enc behavior.

> diff --git a/libavcodec/h261dec.c b/libavcodec/h261dec.c
> index 14a874c45d..3b1711a21d 100644
> --- a/libavcodec/h261dec.c
> +++ b/libavcodec/h261dec.c
> @@ -502,9 +502,9 @@ static int h261_decode_picture_header(H261Context *h)
>      s->avctx->framerate = (AVRational) { 30000, 1001 };
>
>      /* PTYPE starts here */
> -    skip_bits1(&s->gb); /* split screen off */
> -    skip_bits1(&s->gb); /* camera  off */
> -    skip_bits1(&s->gb); /* freeze picture release off */
> +    skip_bits1(&s->gb); /* split screen indicator */
> +    skip_bits1(&s->gb); /* document camera indicator */
> +    h->freeze_picture_release = get_bits1(&s->gb); /* freeze picture release */
>
>      format = get_bits1(&s->gb);
>
> @@ -532,7 +532,8 @@ static int h261_decode_picture_header(H261Context *h)
>
>      /* H.261 has no I-frames, but if we pass AV_PICTURE_TYPE_I for the first
>       * frame, the codec crashes if it does not contain all I-blocks
> -     * (e.g. when a packet is lost). */
> +     * (e.g. when a packet is lost). We will fix the picture type in the
> +     * output frame based on h->freeze_picture_release later. */
>      s->pict_type = AV_PICTURE_TYPE_P;

Why can't you use freeze_picture_release here?

Carl Eugen