Re: [FFmpeg-devel] [PATCH v3 3/7] lavf: APV demuxer

[James Almer <jamrial@gmail.com>]

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On 4/23/2025 5:45 PM, Mark Thompson wrote:
> +static int apv_read_header(AVFormatContext *s)
> +{
> +    AVStream *st;
> +    GetByteContext gbc;
> +    APVHeaderInfo header;
> +    uint8_t buffer[28];
> +    uint32_t au_size, signature, pbu_size;
> +    int err, size;
> +
> +    err = ffio_ensure_seekback(s->pb, sizeof(buffer));

Isn't 28 bytes small enough that a backwards avio_seek() should always 
succeed?

> +    if (err < 0)
> +        return err;
> +    size = avio_read(s->pb, buffer, sizeof(buffer));
> +    if (size < 0)
> +        return size;
> +
> +    bytestream2_init(&gbc, buffer, sizeof(buffer));
> +
> +    au_size = bytestream2_get_be32(&gbc);
> +    if (au_size < 24) {
> +        // Too small.
> +        return AVERROR_INVALIDDATA;
> +    }
> +    signature = bytestream2_get_be32(&gbc);
> +    if (signature != APV_SIGNATURE) {
> +        // Signature is mandatory.
> +        return AVERROR_INVALIDDATA;
> +    }
> +    pbu_size = bytestream2_get_be32(&gbc);
> +    if (pbu_size < 16) {
> +        // Too small.
> +        return AVERROR_INVALIDDATA;
> +    }
> +
> +    err = apv_extract_header_info(&header, &gbc);
> +    if (err < 0)
> +        return err;
> +
> +    st = avformat_new_stream(s, NULL);
> +    if (!st)
> +        return AVERROR(ENOMEM);
> +
> +    st->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
> +    st->codecpar->codec_id   = AV_CODEC_ID_APV;
> +    st->codecpar->format     = header.pixel_format;
> +    st->codecpar->profile    = header.profile_idc;
> +    st->codecpar->level      = header.level_idc;
> +    st->codecpar->width      = header.frame_width;
> +    st->codecpar->height     = header.frame_height;
> +
> +    st->avg_frame_rate = (AVRational){ 30, 1 };
> +    avpriv_set_pts_info(st, 64, 1, 30);
> +
> +    avio_seek(s->pb, -size, SEEK_CUR);
> +
> +    return 0;
> +}
> +
> +static int apv_read_packet(AVFormatContext *s, AVPacket *pkt)
> +{
> +    uint32_t au_size;
> +    int ret;
> +
> +    au_size = avio_rb32(s->pb);
> +    if (au_size == 0 && avio_feof(s->pb))
> +        return AVERROR_EOF;
> +    if (au_size < 16 || au_size > 1 << 24) {

Might be a good idea to also check for the signature.

> +        av_log(s, AV_LOG_ERROR, "APV AU is bad\n");
> +        return AVERROR_INVALIDDATA;
> +    }
> +
> +    ret = av_get_packet(s->pb, pkt, au_size);
> +    pkt->flags        = AV_PKT_FLAG_KEY;
> +
> +    return ret;
> +}


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