[FFmpeg-devel] [PATCH] VQF demuxer

[Michael Niedermayer]

On Sat, Mar 07, 2009 at 05:42:59PM +0100, Vitor Sessak wrote:
> Hi,
>
> See $subj. This is a pretty simple demuxer, the only non-standard thing 
> about it is that a frame size in bits is not always a multiple of 8. I'll 
> post in a separated thread a WIP TwinVQ decoder if anyone wants to test the 
> demuxer (I've tested it with all the samples in ftp.mplayerhq.hu).

patcheck says:

divide by 2^x could use >> maybe
vqf.diff:74:+    return AVPROBE_SCORE_MAX/2;
vqf.diff:223:+    int size = (c->frame_bit_len - c->remaining_bits + 7)/8;
vqf.diff:265:+    if ((ret = url_fseek(s->pb, (pos-7)/8 + s->data_offset, SEEK_SET)) < 0)

Non static with no ff_/av_ prefix
vqf.diff:246:+int vqf_read_seek(AVFormatContext *s,
vqf.diff:272:+AVInputFormat vqf_demuxer = {



[...]
> Index: libavformat/vqf.c
> ===================================================================
> --- libavformat/vqf.c	(revision 0)
> +++ libavformat/vqf.c	(revision 0)
[...]
> +typedef struct VqfContext {
> +    int frame_bit_len;
> +    uint8_t last_frame_bits;
> +    int remaining_bits;
> +} VqfContext;
> +

> +static int vqf_probe(AVProbeData *probe_packet)
> +{
> +    if (probe_packet->buf_size < 12)
> +        return -1;

useless see AVPROBE_PADDING_SIZE



> +
> +    if (AV_RL32(probe_packet->buf) != MKTAG('T','W','I','N'))
> +        return 0;
> +
> +    if (!memcmp(probe_packet->buf + 4, "97012000", 8))
> +        return AVPROBE_SCORE_MAX;
> +
> +    if (!memcmp(probe_packet->buf + 4, "00052200", 8))
> +        return AVPROBE_SCORE_MAX;
> +
> +    return AVPROBE_SCORE_MAX/2;
> +}
> +

> +static void add_metadata(AVFormatContext *s, const char *tag, int tag_len,
> +    int remaining)
> +{
> +    char buf[2048];
> +    int len = FFMIN3(tag_len, remaining, 2047);

 sizeof(buf)-1


> +
> +    if(len != tag_len)
> +        av_log(s, AV_LOG_ERROR, "Warning: truncating metadata!\n");
> +
> +    get_buffer(s->pb, buf, len);
> +    buf[len] = 0;
> +    av_metadata_set(&s->metadata, tag, buf);
> +}
> +

> +static int vqf_read_header(AVFormatContext *s, AVFormatParameters *ap)
> +{
> +    VqfContext *c = s->priv_data;
> +    AVStream *st = av_new_stream(s, 0);
> +    int chunk_tag;
> +    int rate_flag = -1;
> +    int header_size;
> +    int read_bitrate = 0;
> +    int size;
> +
> +    if (!st)
> +        return AVERROR(ENOMEM);
> +
> +    url_fskip(s->pb, 12);
> +
> +    header_size = get_be32(s->pb);
> +

> +    st->codec->codec_type = CODEC_TYPE_AUDIO;
> +    st->codec->codec_id = CODEC_ID_TWINVQ;

vertical align


> +    st->start_time = 0;
> +
> +    do {
> +        int len;
> +        chunk_tag = get_le32(s->pb);
> +
> +        if (chunk_tag == MKTAG('D','A','T','A'))
> +            break;
> +
> +        len = get_be32(s->pb);
> +        header_size -= 8;
> +
> +        switch(chunk_tag){
> +        case MKTAG('C','O','M','M'):
> +            st->codec->channels = get_be32(s->pb) + 1;
> +            read_bitrate        = get_be32(s->pb);
> +            rate_flag           = get_be32(s->pb);
> +            url_fskip(s->pb, len-12);
> +
> +            st->codec->bit_rate = read_bitrate*1000;
> +            st->codec->bits_per_coded_sample = 16;
> +            break;
> +        case MKTAG('N','A','M','E'):
> +            add_metadata(s, "title"    , len, header_size);
> +            break;
> +        case MKTAG('(','c',')',' '):
> +            add_metadata(s, "copyright", len, header_size);
> +            break;
> +        case MKTAG('A','U','T','H'):
> +            add_metadata(s, "author"   , len, header_size);
> +            break;
> +        case MKTAG('A','L','B','M'):
> +            add_metadata(s, "album"    , len, header_size);
> +            break;
> +        case MKTAG('T','R','C','K'):
> +            add_metadata(s, "track"    , len, header_size);
> +            break;
> +        case MKTAG('C','O','M','T'):
> +            add_metadata(s, "comment"  , len, header_size);
> +            break;
> +        case MKTAG('F','I','L','E'):
> +            add_metadata(s, "filename" , len, header_size);
> +            break;
> +        case MKTAG('D','S','I','Z'):
> +            add_metadata(s, "size"     , len, header_size);
> +            break;
> +        case MKTAG('D','A','T','E'):
> +            add_metadata(s, "date"     , len, header_size);
> +            break;
> +        case MKTAG('G','E','N','R'):
> +            add_metadata(s, "genre"    , len, header_size);
> +            break;
> +        default:
> +            av_log(s, AV_LOG_ERROR, "Unknown chunk: %c%c%c%c\n",
> +                   ((char*)&chunk_tag)[0], ((char*)&chunk_tag)[1],
> +                   ((char*)&chunk_tag)[2], ((char*)&chunk_tag)[3]);
> +            url_fskip(s->pb, FFMIN(len,header_size));
> +            break;
> +        }
> +
> +        header_size -= len;
> +
> +    } while(header_size >= 0);

infinite loop given "appropriate" len


[...]
> +    c->frame_bit_len = st->codec->bit_rate*size/st->codec->sample_rate;
> +
> +  return 0;
> +}

indention


> +
> +static int vqf_read_packet(AVFormatContext *s, AVPacket *pkt)
> +{
> +    VqfContext *c = s->priv_data;
> +    int ret;
> +    int size = (c->frame_bit_len - c->remaining_bits + 7)/8;
> +
> +    pkt->pos = url_ftell(s->pb);
> +    pkt->stream_index = 0;
> +
> +    if (av_new_packet(pkt, size+2) < 0)
> +        return AVERROR(EIO);
> +

> +    pkt->data[0] = 8 - c->remaining_bits; // Number of bits to skip
> +    pkt->data[1] = c->last_frame_bits;

wastes 7bit ;)
you could avoid this (iam not suggesting you actually do ..)
by filling the bits to skip by
1   (for 1)
01  (for 2)
...
00000001 (for 8)



[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I have never wished to cater to the crowd; for what I know they do not
approve, and what they approve I do not know. -- Epicurus
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