[FFmpeg-devel] [PATCH] avcodec/decode: port last_pkt_props to AVFifoBuffer

[Andreas Rheinhardt]

James Almer:
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
> The idea of making avpriv_packet_list_* public was not liked, and it was
> suggested to just use AVFifoBuffer instead.
> 
> After this, the avpriv_packet_list_* functions can be made local to
> libavformat again.
> 
>  libavcodec/decode.c   | 41 +++++++++++++++++++++++++++++------------
>  libavcodec/internal.h |  4 ++--
>  libavcodec/utils.c    | 11 ++++++-----
>  3 files changed, 37 insertions(+), 19 deletions(-)
> 
> diff --git a/libavcodec/decode.c b/libavcodec/decode.c
> index 5a1849f944..0550637029 100644
> --- a/libavcodec/decode.c
> +++ b/libavcodec/decode.c
> @@ -145,22 +145,40 @@ fail2:
>  
>  #define IS_EMPTY(pkt) (!(pkt)->data)
>  
> +static int copy_packet_props(void *_src, void *_dst, int size)
> +{
> +    AVPacket *src = _src, *dst = _dst;
> +    int ret;
> +
> +    av_init_packet(dst);
> +    ret = av_packet_copy_props(dst, src);
> +    if (ret < 0)
> +        return ret;> +
> +    dst->size = src->size; // HACK: Needed for ff_decode_frame_props().
> +    dst->data = (void*)1;  // HACK: Needed for IS_EMPTY().
> +
> +    return sizeof(*dst);
> +}

This is not how a write function for a fifo should look like: A fifo may
need to store the beginning of a packet at the end of the fifo and the
end of a packet at the beginning of a fifo; you can check for this by
checking whether size is < sizeof(AVPacket).
(The current implementation seems to actually only allocate multiples of
a certain unit if all av_fifo_grow()/av_fifo_realloc2()/av_fifo_alloc()
calls use only multiples of this unit, but it doesn't seem to be
documented. Should probably be done as this simplifies using fifo arrays.)

And apart from that: The current implementation of
av_fifo_generic_write() does not forward errors from the write function;
and changing this require be an API break.

> +
>  static int extract_packet_props(AVCodecInternal *avci, AVPacket *pkt)
>  {
>      int ret = 0;
>  
> -    ret = avpriv_packet_list_put(&avci->pkt_props, &avci->pkt_props_tail, pkt,
> -                                 av_packet_copy_props, 0);
> +    if (av_fifo_space(avci->pkt_props) < sizeof(*pkt)) {
> +        ret = av_fifo_grow(avci->pkt_props, sizeof(*pkt));
> +        if (ret < 0)
> +            return ret;
> +    }
> +
> +    ret = av_fifo_generic_write(avci->pkt_props, pkt, sizeof(*pkt), copy_packet_props);
>      if (ret < 0)
>          return ret;
> -    avci->pkt_props_tail->pkt.size = pkt->size; // HACK: Needed for ff_decode_frame_props().
> -    avci->pkt_props_tail->pkt.data = (void*)1;  // HACK: Needed for IS_EMPTY().
>  
> +    av_assert0(ret == sizeof(*pkt));
>      if (IS_EMPTY(avci->last_pkt_props)) {
> -        ret = avpriv_packet_list_get(&avci->pkt_props,
> -                                     &avci->pkt_props_tail,
> -                                     avci->last_pkt_props);
> -        av_assert0(ret != AVERROR(EAGAIN));
> +        ret = av_fifo_generic_read(avci->pkt_props, avci->last_pkt_props,
> +                                   sizeof(*avci->last_pkt_props), NULL);
>      }
>      return ret;
>  }
> @@ -1721,10 +1739,9 @@ int ff_decode_frame_props(AVCodecContext *avctx, AVFrame *frame)
>          { AV_PKT_DATA_S12M_TIMECODE,              AV_FRAME_DATA_S12M_TIMECODE },
>      };
>  
> -    if (IS_EMPTY(pkt))
> -        avpriv_packet_list_get(&avctx->internal->pkt_props,
> -                               &avctx->internal->pkt_props_tail,
> -                               pkt);
> +    if (IS_EMPTY(pkt) && av_fifo_size(avctx->internal->pkt_props) >= sizeof(*pkt))
> +        av_fifo_generic_read(avctx->internal->pkt_props,
> +                             pkt, sizeof(*pkt), NULL);
>  
>      if (pkt) {
>          frame->pts = pkt->pts;
> diff --git a/libavcodec/internal.h b/libavcodec/internal.h
> index 17defb9b50..8a51bca2df 100644
> --- a/libavcodec/internal.h
> +++ b/libavcodec/internal.h
> @@ -28,6 +28,7 @@
>  
>  #include "libavutil/buffer.h"
>  #include "libavutil/channel_layout.h"
> +#include "libavutil/fifo.h"
>  #include "libavutil/mathematics.h"
>  #include "libavutil/pixfmt.h"
>  #include "avcodec.h"
> @@ -145,8 +146,7 @@ typedef struct AVCodecInternal {
>       * for decoding.
>       */
>      AVPacket *last_pkt_props;
> -    AVPacketList *pkt_props;
> -    AVPacketList *pkt_props_tail;
> +    AVFifoBuffer *pkt_props;
>  
>      /**
>       * temporary buffer used for encoders to store their bitstream
> diff --git a/libavcodec/utils.c b/libavcodec/utils.c
> index 45295dd3ce..c81cc972dc 100644
> --- a/libavcodec/utils.c
> +++ b/libavcodec/utils.c
> @@ -593,10 +593,12 @@ int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
>      avci->es.in_frame = av_frame_alloc();
>      avci->ds.in_pkt = av_packet_alloc();
>      avci->last_pkt_props = av_packet_alloc();
> +    avci->pkt_props = av_fifo_alloc(sizeof(AVPacket));
>      if (!avci->compat_decode_frame || !avci->compat_encode_packet ||
>          !avci->buffer_frame || !avci->buffer_pkt          ||
>          !avci->es.in_frame  || !avci->ds.in_pkt           ||
> -        !avci->to_free      || !avci->last_pkt_props) {
> +        !avci->to_free      || !avci->last_pkt_props      ||
> +        !avci->pkt_props) {
>          ret = AVERROR(ENOMEM);
>          goto free_and_end;
>      }
> @@ -1076,6 +1078,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
>      av_packet_free(&avci->compat_encode_packet);
>      av_packet_free(&avci->buffer_pkt);
>      av_packet_free(&avci->last_pkt_props);
> +    av_fifo_freep(&avci->pkt_props);
>  
>      av_packet_free(&avci->ds.in_pkt);
>      av_frame_free(&avci->es.in_frame);
> @@ -1116,8 +1119,7 @@ void avcodec_flush_buffers(AVCodecContext *avctx)
>      av_packet_unref(avci->buffer_pkt);
>  
>      av_packet_unref(avci->last_pkt_props);
> -    avpriv_packet_list_free(&avci->pkt_props,
> -                            &avci->pkt_props_tail);
> +    av_fifo_reset(avci->pkt_props);
>  

The packets in the fifo may contain side-data (because
av_packet_copy_props() copies it) and if so, it leaks here.

>      av_frame_unref(avci->es.in_frame);
>      av_packet_unref(avci->ds.in_pkt);
> @@ -1180,8 +1182,7 @@ av_cold int avcodec_close(AVCodecContext *avctx)
>          av_packet_free(&avctx->internal->compat_encode_packet);
>          av_packet_free(&avctx->internal->buffer_pkt);
>          av_packet_free(&avctx->internal->last_pkt_props);
> -        avpriv_packet_list_free(&avctx->internal->pkt_props,
> -                                &avctx->internal->pkt_props_tail);
> +        av_fifo_freep(&avctx->internal->pkt_props);
>  
>          av_packet_free(&avctx->internal->ds.in_pkt);
>          av_frame_free(&avctx->internal->es.in_frame);
>