[FFmpeg-devel] [PATCH] OSQ lossless audio format support

[James Almer]

On 8/24/2023 6:52 AM, Paul B Mahol wrote:
> +static int osq_receive_frame(AVCodecContext *avctx, AVFrame *frame)
> +{
> +    OSQContext *s = avctx->priv_data;
> +    GetBitContext *gb = &s->gb;
> +    int ret, n;
> +
> +    while (s->bitstream_size < s->max_framesize) {
> +        int size;
> +
> +        if (!s->pkt->data) {
> +            ret = ff_decode_get_packet(avctx, s->pkt);
> +            if (ret == AVERROR_EOF && s->bitstream_size > 0)
> +                break;
> +            if (ret < 0)
> +                return ret;
> +        }
> +
> +        size = FFMIN(s->pkt->size - s->pkt_offset, s->max_framesize - s->bitstream_size);
> +        memcpy(s->bitstream + s->bitstream_size, s->pkt->data + s->pkt_offset, size);
> +        s->bitstream_size += size;
> +        s->pkt_offset += size;
> +
> +        if (s->pkt_offset == s->pkt->size) {
> +            av_packet_unref(s->pkt);
> +            s->pkt_offset = 0;
> +        }

This looks like you're assembling a packet of max_framesize bytes. You 
should instead do that in a parser, and ensure here that the packets fed 
to this decoder are <= max_framesize.

> +    }
> +
> +    frame->nb_samples = FFMIN(s->frame_samples, s->nb_samples);
> +    if (frame->nb_samples <= 0)
> +        return AVERROR_EOF;
> +
> +    if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
> +        goto fail;
> +
> +    if ((ret = init_get_bits8(gb, s->bitstream, s->bitstream_size)) < 0)
> +        goto fail;
> +
> +    if ((ret = osq_decode_block(avctx, frame)) < 0)
> +        goto fail;
> +
> +    s->nb_samples -= frame->nb_samples;
> +
> +    n = get_bits_count(gb) / 8;
> +    if (n > s->bitstream_size) {
> +        ret = AVERROR_INVALIDDATA;
> +        goto fail;
> +    }
> +
> +    memmove(s->bitstream, &s->bitstream[n], s->bitstream_size - n);
> +    s->bitstream_size -= n;
> +
> +    return 0;
> +
> +fail:
> +    s->bitstream_size = 0;
> +    s->pkt_offset = 0;
> +    av_packet_unref(s->pkt);
> +
> +    return ret;
> +}
> +
> +const AVInputFormat ff_osq_demuxer = {
> +    .name           = "osq",
> +    .long_name      = NULL_IF_CONFIG_SMALL("raw OSQ"),
> +    .read_probe     = osq_probe,
> +    .read_header    = osq_read_header,
> +    .read_packet    = ff_raw_read_partial_packet,

Instead of sending an arbitrarily sized packet (1024 bytes as of now), 
you should set codecpar->frame_size and propagate packets with that 
amount of bytes instead.
A parser is still needed, though, for non seekable input (a pipe). And 
in case the decoder is fed with non lavf input.

> +    .extensions     = "osq",
> +    .flags          = AVFMT_NOBINSEARCH | AVFMT_NOGENSEARCH | AVFMT_NO_BYTE_SEEK | AVFMT_NOTIMESTAMPS,
> +    .raw_codec_id   = AV_CODEC_ID_OSQ,
> +    .priv_data_size = sizeof(FFRawDemuxerContext),
> +    .priv_class     = &ff_raw_demuxer_class,
> +};