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

[James Almer]

On 8/24/2023 6:11 PM, Paul B Mahol wrote:
> On Thu, Aug 24, 2023 at 11:00 PM James Almer <jamrial at gmail.com> wrote:
> 
>> 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.
>>
> 
> Format is not seekable, packet sizes are nowhere stored in .osq files.

Same case as raw formats like H.264. No packet sizes, no seekability 
without having parsed the entire sequence to build a list of seek 
points, etc. A parser has to assemble access units.

> 
> Think of this format like APAC/BONK/WAVARC but just no need to keep unused
> bits from previous decoded data/packet.
> With this fact, parser makes no sense to do.

You know that frame_size is (frame_samples_per_channel * 16 + 1024) * 
channels. A parser can work with that (Look at gsm parser for example. 
There may be others too).
You should not propagate truncated data in 1024 byte chunks, and the 
decoder should not expect that either.

> 
> 
>>> +    .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,
>>> +};
>>
>> _______________________________________________
>> ffmpeg-devel mailing list
>> ffmpeg-devel at ffmpeg.org
>> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>>
>> To unsubscribe, visit link above, or email
>> ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".
>>
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> 
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".