[FFmpeg-devel] [PATCH 2/2] Add experimental demuxing support for FLAC in ISO BMFF (MP4).

[James Almer]

On 10/31/2016 3:27 AM, Matthew Gregan wrote:
> Based on the draft spec at https://git.xiph.org/?p=flac.git;a=blob;f=doc/isoflac.txt
> 
> Signed-off-by: Matthew Gregan <kinetik at flim.org>
> ---
>  libavformat/mov.c | 41 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 41 insertions(+)
> 
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index 357d800..fc36b0e 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -4684,6 +4684,46 @@ static int mov_read_saiz(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>      return 0;
>  }
>  
> +static int mov_read_dfla(MOVContext *c, AVIOContext *pb, MOVAtom atom)
> +{
> +    const size_t FLAC_STREAMINFO_SIZE = 34;

Just include libavcodec/flac.h which already defines it.

> +    AVStream *st;
> +    uint8_t type;
> +    size_t size;
> +
> +    if (c->fc->nb_streams < 1)
> +        return 0;
> +    st = c->fc->streams[c->fc->nb_streams-1];
> +
> +    if ((uint64_t)atom.size > (1<<30) || atom.size < 42)
> +        return AVERROR_INVALIDDATA;
> +
> +    /* Check FlacSpecificBox version. */
> +    if (avio_r8(pb) != 0)
> +        return AVERROR_INVALIDDATA;
> +
> +    avio_rb24(pb); /* Flags */
> +
> +    type = avio_r8(pb);
> +    /* TODO: Read other METADATA_BLOCK_TYPEs if the decoder wants them. */
> +    if (!(type & 0x80)) {
> +      av_log(c->fc, AV_LOG_WARNING, "ignoring non-STREAMINFO FLACMetadataBlocks\n");
> +    }
> +    type = type & 0x7f;
> +    size = avio_rb24(pb);

With the above header you'll also be able to use the inline function
flac_parse_block_header() for this. See flac and matroska demuxers.

> +
> +    /* The first METADATA_BLOCK_TYPE must be STREAMINFO. */
> +    if (type != 0 || size != FLAC_STREAMINFO_SIZE)
> +        return AVERROR_INVALIDDATA;

INVALIDDATA errors would ideally also throw an error message.

> +
> +    if (ff_alloc_extradata(st->codecpar, size))
> +        return AVERROR(ENOMEM);
> +
> +    avio_read(pb, st->codecpar->extradata, size);

Use ff_get_extradata(), which combines these two into a single function.

> +
> +    return 0;
> +}
> +
>  static int cenc_filter(MOVContext *c, MOVStreamContext *sc, uint8_t *input, int size)
>  {
>      uint32_t encrypted_bytes;
> @@ -4858,6 +4898,7 @@ static const MOVParseTableEntry mov_default_parse_table[] = {
>  { MKTAG('f','r','m','a'), mov_read_frma },
>  { MKTAG('s','e','n','c'), mov_read_senc },
>  { MKTAG('s','a','i','z'), mov_read_saiz },
> +{ MKTAG('d','f','L','a'), mov_read_dfla },
>  { 0, NULL }
>  };
>  
>