[FFmpeg-devel] [PATCH] avformat/cafdec: Implement FLAC-in-CAF parsing

[Andreas Rheinhardt]

Martijn van Beurden:
> The afconvert utility shipped with MacOS supports muxing of FLAC
> in CAF, see afconvert help output on a recent Mac here:
> https://hydrogenaud.io/index.php?topic=122509.0 A file created
> with afconvert free of copyright (licensed CC0) can be found here:
> http://www.audiograaf.nl/misc_stuff/afconvert-FLAC-in-CAF.caf
> 
> This patch implements parsing of such a file
> ---
>  libavformat/caf.c    |  1 +
>  libavformat/cafdec.c | 41 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 42 insertions(+)
> 
> diff --git a/libavformat/caf.c b/libavformat/caf.c
> index a700e4055b..a61c39fae5 100644
> --- a/libavformat/caf.c
> +++ b/libavformat/caf.c
> @@ -46,6 +46,7 @@ const AVCodecTag ff_codec_caf_tags[] = {
>      { AV_CODEC_ID_GSM,             MKTAG('a','g','s','m') },
>      { AV_CODEC_ID_GSM_MS,          MKTAG('m','s', 0, '1') },
>      { AV_CODEC_ID_ILBC,            MKTAG('i','l','b','c') },
> +    { AV_CODEC_ID_FLAC,            MKTAG('f','l','a','c') },
>      { AV_CODEC_ID_MACE3,           MKTAG('M','A','C','3') },
>      { AV_CODEC_ID_MACE6,           MKTAG('M','A','C','6') },
>      { AV_CODEC_ID_MP1,             MKTAG('.','m','p','1') },
> diff --git a/libavformat/cafdec.c b/libavformat/cafdec.c
> index 168f69f20b..72a74ab297 100644
> --- a/libavformat/cafdec.c
> +++ b/libavformat/cafdec.c
> @@ -31,6 +31,7 @@
>  #include "demux.h"
>  #include "internal.h"
>  #include "isom.h"
> +#include "libavcodec/flac.h"
>  #include "mov_chan.h"
>  #include "libavutil/intreadwrite.h"
>  #include "libavutil/intfloat.h"
> @@ -170,6 +171,46 @@ static int read_kuki_chunk(AVFormatContext *s, int64_t size)
>              }
>              avio_skip(pb, size - ALAC_NEW_KUKI);
>          }
> +    } else if (st->codecpar->codec_id == AV_CODEC_ID_FLAC) {
> +        int last, type, flac_metadata_size;
> +        uint8_t buf[4];
> +        /* The magic cookie format for FLAC consists mostly of an mp4 dfLa atom. */
> +        if (size < (16 + FLAC_STREAMINFO_SIZE)) {
> +            av_log(s, AV_LOG_ERROR, "invalid FLAC magic cookie\n");
> +            return AVERROR_INVALIDDATA;
> +        }
> +        /* Check cookie version. */
> +        if (avio_r8(pb) != 0) {
> +            av_log(s, AV_LOG_ERROR, "unknown FLAC magic cookie\n");
> +            return AVERROR_INVALIDDATA;
> +        }
> +        avio_rb24(pb); /* Flags */
> +        /* read dfLa fourcc */
> +        if (avio_read(pb, buf, 4) != 4) {
> +            av_log(s, AV_LOG_ERROR, "failed to read FLAC magic cookie\n");
> +            return AVERROR_INVALIDDATA;
> +        }
> +        if (memcmp(buf,"dfLa",4)) {
> +            av_log(s, AV_LOG_ERROR, "invalid FLAC magic cookie\n");
> +            return AVERROR_INVALIDDATA;
> +        }
> +        /* Check dfLa version. */
> +        if (avio_r8(pb) != 0) {
> +            av_log(s, AV_LOG_ERROR, "unknown dfLa version\n");
> +            return AVERROR_INVALIDDATA;
> +        }
> +        avio_rb24(pb); /* Flags */
> +        avio_read(pb, buf, sizeof(buf));

You are not checking this; this could lead to uninitialized values being
used in flac_parse_block_header() below.

> +        flac_parse_block_header(buf, &last, &type, &flac_metadata_size);
> +        if (type != FLAC_METADATA_TYPE_STREAMINFO || flac_metadata_size != FLAC_STREAMINFO_SIZE) {
> +            av_log(s, AV_LOG_ERROR, "STREAMINFO must be first FLACMetadataBlock\n");
> +            return AVERROR_INVALIDDATA;
> +        }
> +        ret = ff_get_extradata(s, st->codecpar, pb, FLAC_STREAMINFO_SIZE);
> +        if (ret < 0)
> +            return ret;
> +        if (!last)
> +            av_log(s, AV_LOG_WARNING, "non-STREAMINFO FLACMetadataBlock(s) ignored\n");
>      } else if (st->codecpar->codec_id == AV_CODEC_ID_OPUS) {
>          // The data layout for Opus is currently unknown, so we do not export
>          // extradata at all. Multichannel streams are not supported.

Is there an official spec for this?

- Andreas