Re: [FFmpeg-devel] [PATCH v3 1/2] lavf/mpegenc: fix ever-growing fifo size since the new API

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Nicolas Gaullier:
> The older av_fifo_realloc2 implemented an auto grow that
> should be ported as such in the new API.
> 
> This patch introduces a limitation in the fifo buffer size.
> The default is set to 128MB and may be overriden by a new user option.
> The amount of memory allocated depends on multiple factors, including
> the number of audio streams.
> A worst case scenario is where an out-of-spec high video bitrate is
> combined with numerous low bitrate audios.
> 
> Fix regressing since ea511196a6c85eb433e10cdbecb0b2c722faf20d
> 
> Signed-off-by: Nicolas Gaullier <nicolas.gaullier@cji.paris>
> ---
>  libavformat/mpegenc.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/libavformat/mpegenc.c b/libavformat/mpegenc.c
> index cc47a43288..5d755e3bdd 100644
> --- a/libavformat/mpegenc.c
> +++ b/libavformat/mpegenc.c
> @@ -84,6 +84,7 @@ typedef struct MpegMuxContext {
>      int64_t vcd_padding_bytes_written;
>  
>      int preload;
> +    uint32_t fifo_size_limit;
>  } MpegMuxContext;
>  
>  extern const AVOutputFormat ff_mpeg1vcd_muxer;
> @@ -461,9 +462,10 @@ static av_cold int mpeg_mux_init(AVFormatContext *ctx)
>                     av_get_media_type_string(st->codecpar->codec_type), i);
>              return AVERROR(EINVAL);
>          }
> -        stream->fifo = av_fifo_alloc2(16, 1, 0);
> +        stream->fifo = av_fifo_alloc2(16, 1, AV_FIFO_FLAG_AUTO_GROW);
>          if (!stream->fifo)
>              return AVERROR(ENOMEM);
> +        av_fifo_auto_grow_limit(stream->fifo, s->fifo_size_limit);
>      }
>      bitrate       = 0;
>      audio_bitrate = 0;
> @@ -1151,7 +1153,7 @@ static int mpeg_mux_write_packet(AVFormatContext *ctx, AVPacket *pkt)
>      StreamInfo *stream = st->priv_data;
>      int64_t pts, dts;
>      PacketDesc *pkt_desc;
> -    int preload, ret;
> +    int preload;
>      const int is_iframe = st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
>                            (pkt->flags & AV_PKT_FLAG_KEY);
>  
> @@ -1207,10 +1209,6 @@ static int mpeg_mux_write_packet(AVFormatContext *ctx, AVPacket *pkt)
>      pkt_desc->unwritten_size =
>      pkt_desc->size           = size;
>  
> -    ret = av_fifo_grow2(stream->fifo, size);
> -    if (ret < 0)
> -        return ret;
> -
>      if (s->is_dvd) {
>          // min VOBU length 0.4 seconds (mpucoder)
>          if (is_iframe &&
> @@ -1277,6 +1275,7 @@ static void mpeg_mux_deinit(AVFormatContext *ctx)
>  static const AVOption options[] = {
>      { "muxrate", NULL,                                          OFFSET(user_mux_rate), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, ((1<<22) - 1) * (8 * 50), E },
>      { "preload", "Initial demux-decode delay in microseconds.", OFFSET(preload),  AV_OPT_TYPE_INT, { .i64 = 500000 }, 0, INT_MAX, E },
> +    { "fifo_size_limit", "Maximum allowed memory for buffering an input stream in bytes", OFFSET(fifo_size_limit), AV_OPT_TYPE_INT, {.i64 = 128 * 1024 * 1024 }, 0, UINT_MAX, E},
>      { NULL },
>  };
>  

1. Options of type AV_OPT_TYPE_INT need to have a target of type int.
2. Setting UINT_MAX as maximum for such an option is nonsense; INT_MAX
is the maximum for it. (FFMIN(INT_MAX, SIZE_MAX) would be even better.)
3. Allowing zero for fifo_size_limit makes no sense, as the above code
allocates 16 when allocating the FIFO.
4. After removing av_fifo_grow2() it is no longer assured that
av_fifo_write() succeeds; it therefore needs to be checked.

- Andreas
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