[FFmpeg-devel] [PATCH] avformat/westwood_vqa: Store VQFL codebook chunks

[Andreas Rheinhardt]

Pekka Väänänen:
> High color 15-bit VQA3 video streams contain high level chunks with
> only codebook updates that shouldn't be considered new frames. Now
> the demuxer stores a reference to such VQFL chunks and returns them
> later along with a VQFR chunk with full frame data.
> ---
>  libavformat/westwood_vqa.c | 51 ++++++++++++++++++++++++++++++++++++--
>  1 file changed, 49 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/westwood_vqa.c b/libavformat/westwood_vqa.c
> index 77df007c11..cc859c58ca 100644
> --- a/libavformat/westwood_vqa.c
> +++ b/libavformat/westwood_vqa.c
> @@ -1,6 +1,7 @@
>  /*
>   * Westwood Studios VQA Format Demuxer
> - * Copyright (c) 2003 The FFmpeg project
> + * Copyright (c) 2003 Mike Melanson <melanson at pcisys.net>
> + * Copyright (c) 2021 Pekka Väänänen <pekka.vaananen at iki.fi>
>   *
>   * This file is part of FFmpeg.
>   *
> @@ -30,6 +31,7 @@
>  
>  #include "libavutil/intreadwrite.h"
>  #include "avformat.h"
> +#include "avio_internal.h"
>  #include "internal.h"
>  
>  #define FORM_TAG MKBETAG('F', 'O', 'R', 'M')
> @@ -40,6 +42,7 @@
>  #define SND1_TAG MKBETAG('S', 'N', 'D', '1')
>  #define SND2_TAG MKBETAG('S', 'N', 'D', '2')
>  #define VQFR_TAG MKBETAG('V', 'Q', 'F', 'R')
> +#define VQFL_TAG MKBETAG('V', 'Q', 'F', 'L')
>  
>  /* don't know what these tags are for, but acknowledge their existence */
>  #define CINF_TAG MKBETAG('C', 'I', 'N', 'F')
> @@ -60,6 +63,8 @@ typedef struct WsVqaDemuxContext {
>      int sample_rate;
>      int audio_stream_index;
>      int video_stream_index;
> +    int64_t vqfl_chunk_pos;
> +    int vqfl_chunk_size;
>  } WsVqaDemuxContext;
>  
>  static int wsvqa_probe(const AVProbeData *p)
> @@ -120,6 +125,8 @@ static int wsvqa_read_header(AVFormatContext *s)
>      wsvqa->channels     = header[26];
>      wsvqa->bps          = header[27];
>      wsvqa->audio_stream_index = -1;
> +    wsvqa->vqfl_chunk_pos     = 0;
> +    wsvqa->vqfl_chunk_size    = 0;
>  
>      s->ctx_flags |= AVFMTCTX_NOHEADER;
>  
> @@ -172,7 +179,21 @@ static int wsvqa_read_packet(AVFormatContext *s,
>  
>          skip_byte = chunk_size & 0x01;
>  
> -        if ((chunk_type == SND0_TAG) || (chunk_type == SND1_TAG) ||
> +        if (chunk_type == VQFL_TAG) {
> +            /* Each VQFL chunk carries only a codebook update inside which must be applied
> +             * before the next VQFR is rendered. That's why we stash the VQFL offset here
> +             * so it can be combined with the next VQFR packet. This way each packet
> +             * includes a whole frame as expected. */
> +            wsvqa->vqfl_chunk_pos = avio_tell(pb);
> +            wsvqa->vqfl_chunk_size = (int)(chunk_size);
> +            if (wsvqa->vqfl_chunk_size < 0 || wsvqa->vqfl_chunk_size > 3 * (1 << 20))
> +                return AVERROR_INVALIDDATA;
> +            /* We need a big seekback buffer because there can be SNxx, VIEW and ZBUF
> +             * chunks in the stream before we reach VQFR and seek back here. */

This code also reads the VQFR chunk before seeking back, so this needs
to be changed or accounted for.

> +            ffio_ensure_seekback(pb, wsvqa->vqfl_chunk_size + 512 * 1024);
> +            avio_skip(pb, chunk_size + skip_byte);
> +            continue;
> +        } else if ((chunk_type == SND0_TAG) || (chunk_type == SND1_TAG) ||
>              (chunk_type == SND2_TAG) || (chunk_type == VQFR_TAG)) {
>  
>              ret= av_get_packet(pb, pkt, chunk_size);
> @@ -235,6 +256,32 @@ static int wsvqa_read_packet(AVFormatContext *s,
>                  }
>                  break;
>              case VQFR_TAG:
> +                /* if a new codebook is available inside an earlier a VQFL chunk then
> +                 * prepend it to 'pkt' */
> +                if (wsvqa->vqfl_chunk_size > 0) {
> +                    int64_t current_pos = pkt->pos;
> +                    int current_size = pkt->size;
> +
> +                    if (avio_seek(pb, wsvqa->vqfl_chunk_pos, SEEK_SET) < 0)
> +                        return AVERROR(EIO);
> +
> +                    /* the decoder expects chunks to be 16-bit aligned */
> +                    if (wsvqa->vqfl_chunk_size % 2 == 1)
> +                        wsvqa->vqfl_chunk_size++;
> +
> +                    av_packet_unref(pkt);

This fixes the memleak, yet the main data is still read twice.

> +                    if (av_get_packet(pb, pkt, wsvqa->vqfl_chunk_size) < 0)
> +                        return AVERROR(EIO);
> +
> +                    if (avio_seek(pb, current_pos, SEEK_SET) < 0)
> +                        return AVERROR(EIO);
> +
> +                    ret = av_append_packet(pb, pkt, current_size);
> +
> +                    wsvqa->vqfl_chunk_pos = 0;
> +                    wsvqa->vqfl_chunk_size = 0;
> +                }
> +
>                  pkt->stream_index = wsvqa->video_stream_index;
>                  pkt->duration = 1;
>                  break;
>