[FFmpeg-devel] [PATCH] oma demuxer

[Michael Niedermayer]

On Mon, May 05, 2008 at 10:14:35PM +0200, Benjamin Larsson wrote:
> Hi, here is a demuxer for the oma container. Sample file to test the
> decoder can be found here:
> 
> http://samples.mplayerhq.hu/oma/01-Untitled(1).oma
> 

> It works but spits out lots "Multiple frames in a packet" messages. What
> has to be done to fix that issue.

Pass single packets instead of 4 at a time but thats obvious you even 
explicitly multiply by 4.

[...]
> +typedef struct {

> +    int   filesize;

unneeded


> +    int   packetsize;

redundant


> +    int   npackets;

unused


> +    int   datapos;

unneeded


> +} OMAContext;
> +

> +typedef struct {
> +    int   index;
> +    int   bitrate;
> +    int   framesize;
> +    int   channels;
> +    int   coding_mode;
> +} ATRAC3ModeDesc;
> +
> +static const ATRAC3ModeDesc  atrac3_modes[4] = {
> +    {0, 66000, 192, 2, 1},
> +    {1, 94000, 272, 2, 1},
> +    {2, 105000, 304, 2, 0},
> +    {3, 132000, 384, 2, 0}
> +};

this could be an anonymous struct
int is not needed, smaller types are enough
one field equals the index one is const


> +
> +static int is_ea3_tag_header(const uint8_t *buf)
> +{
> +    return (buf[0] == 'e' && buf[1] == 'a' && buf[2] == '3' && buf[3] == 3 && buf[4] == 0);
> +}

strcmp, memcmp, whatever


> +

> +static int16_t get_encryption_id(const uint8_t *buf)
> +{
> +    return (buf[0] << 8 | buf[1]);
> +}

we have code to read 16bits


[...]
> +static int oma_read_header(AVFormatContext *s,
> +                           AVFormatParameters *ap)
> +{
> +    int     filesize, ret, taglen, pos, codec_id, framesize, i, mode;
> +    int16_t eid;
> +    uint8_t buf[EA3_HEADER_SIZE];
> +    const uint8_t *edata;
> +    AVStream *st;
> +    OMAContext *ctx = s->priv_data;
> +

> +    filesize = url_fsize(s->pb);
> +    if (filesize < 10)
> +        return -1;

remove this


[...]
> +    st->codec->channels = atrac3_modes[mode].channels;
> +    st->codec->sample_rate = 44100;
> +    st->codec->bit_rate = atrac3_modes[mode].bitrate;
> +    st->codec->block_align = atrac3_modes[mode].framesize;

vertical align 


> +
> +    /* fake the atrac3 extradata */
> +    st->codec->extradata_size = 14;
> +    edata = av_mallocz(14 + FF_INPUT_BUFFER_PADDING_SIZE);
> +    if (!edata)
> +        return AVERROR(ENOMEM);
> +
> +    st->codec->extradata = edata;
> +    bytestream_put_le16(&edata, 1);
> +    bytestream_put_le32(&edata, 4096);  // samples_per_channel
> +    bytestream_put_le16(&edata, atrac3_modes[mode].coding_mode);
> +    bytestream_put_le16(&edata, atrac3_modes[mode].coding_mode);
> +    bytestream_put_le16(&edata, 1);

> +    bytestream_put_le16(&edata, 0);

redundant



> +
> +    st->need_parsing = AVSTREAM_PARSE_FULL;

This does not work as there is no ATRAC3 parser


[...]
> +static int oma_read_packet(AVFormatContext *s, AVPacket *pkt)
> +{
> +    int ret, size, left;
> +    OMAContext *ctx = s->priv_data;
> +
> +    size = ctx->packetsize * 4;
> +    left = ctx->filesize - url_ftell(s->pb);
> +    if (left < size)
> +        size = left;
> +
> +    ret= av_get_packet(s->pb, pkt, size);
> +
> +    pkt->stream_index = 0;
> +    if (ret <= 0) {
> +        return AVERROR(EIO);
> +    }
> +    /* note: we need to modify the packet size here to handle the last
> +       packet */

> +    pkt->size = ret;

?


> +    return ret;
> +}
> +

> +#ifdef CONFIG_OMA_DEMUXER
> +AVInputFormat oma_demuxer = {
> +    "oma",
> +    "Sony OpenMG audio",
> +    sizeof(OMAContext),
> +    oma_read_probe,
> +    oma_read_header,
> +    oma_read_packet,
> +    NULL,
> +    .flags= AVFMT_GENERIC_INDEX,

> +    .extensions = "oma,aa3", /* XXX: use probe */

senseles as a probe function exists.


> +};
> +#endif

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-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Its not that you shouldnt use gotos but rather that you should write
readable code and code with gotos often but not always is less readable
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