[FFmpeg-devel] [PATCH 1/2] Add experimental muxing support for FLAC in ISO BMFF (MP4).

[Matthew Gregan]

Based on the draft spec at https://git.xiph.org/?p=flac.git;a=blob;f=doc/isoflac.txt

'-strict -2' is required to create files in this format.

Signed-off-by: Matthew Gregan <kinetik at flim.org>
---
 libavformat/isom.c   |  2 ++
 libavformat/movenc.c | 43 +++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/libavformat/isom.c b/libavformat/isom.c
index ab79e22..aacbe43 100644
--- a/libavformat/isom.c
+++ b/libavformat/isom.c
@@ -60,6 +60,7 @@ const AVCodecTag ff_mp4_obj_type[] = {
     { AV_CODEC_ID_EAC3        , 0xA6 },
     { AV_CODEC_ID_DTS         , 0xA9 }, /* mp4ra.org */
     { AV_CODEC_ID_VP9         , 0xC0 }, /* nonstandard, update when there is a standard value */
+    { AV_CODEC_ID_FLAC        , 0xC1 }, /* nonstandard, update when there is a standard value */
     { AV_CODEC_ID_TSCC2       , 0xD0 }, /* nonstandard, camtasia uses it */
     { AV_CODEC_ID_VORBIS      , 0xDD }, /* nonstandard, gpac uses it */
     { AV_CODEC_ID_DVD_SUBTITLE, 0xE0 }, /* nonstandard, see unsupported-embedded-subs-2.mp4 */
@@ -345,6 +346,7 @@ const AVCodecTag ff_codec_movaudio_tags[] = {
     { AV_CODEC_ID_WMAV2,           MKTAG('W', 'M', 'A', '2') },
     { AV_CODEC_ID_EVRC,            MKTAG('s', 'e', 'v', 'c') }, /* 3GPP2 */
     { AV_CODEC_ID_SMV,             MKTAG('s', 's', 'm', 'v') }, /* 3GPP2 */
+    { AV_CODEC_ID_FLAC,            MKTAG('f', 'L', 'a', 'C') }, /* nonstandard */
     { AV_CODEC_ID_NONE, 0 },
 };
 
diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 6228192..d77250e 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -654,6 +654,27 @@ static int mov_write_wfex_tag(AVFormatContext *s, AVIOContext *pb, MOVTrack *tra
     return update_size(pb, pos);
 }
 
+static int mov_write_dfla_tag(AVIOContext *pb, MOVTrack *track)
+{
+    const size_t FLAC_STREAMINFO_SIZE = 34;
+    int64_t pos = avio_tell(pb);
+    avio_wb32(pb, 0);
+    ffio_wfourcc(pb, "dfLa");
+    avio_w8(pb, 0); /* version */
+    avio_wb24(pb, 0); /* flags */
+
+    /* Expect the encoder to pass a METADATA_BLOCK_TYPE_STREAMINFO. */
+    if (track->par->extradata_size != FLAC_STREAMINFO_SIZE)
+      return AVERROR_INVALIDDATA;
+
+    /* TODO: Write other METADATA_BLOCK_TYPEs if the encoder makes them available. */
+    avio_w8(pb, 1 << 7 | 0); /* LastMetadataBlockFlag << 7 | BlockType (STREAMINFO) */
+    avio_wb24(pb, track->par->extradata_size); /* Length */
+    avio_write(pb, track->par->extradata, track->par->extradata_size); /* BlockData[Length] */
+
+    return update_size(pb, pos);
+}
+
 static int mov_write_chan_tag(AVFormatContext *s, AVIOContext *pb, MOVTrack *track)
 {
     uint32_t layout_tag, bitmap;
@@ -963,8 +984,13 @@ static int mov_write_audio_tag(AVFormatContext *s, AVIOContext *pb, MOVMuxContex
                 avio_wb16(pb, 16);
             avio_wb16(pb, track->audio_vbr ? -2 : 0); /* compression ID */
         } else { /* reserved for mp4/3gp */
-            avio_wb16(pb, 2);
-            avio_wb16(pb, 16);
+            if (track->par->codec_id == AV_CODEC_ID_FLAC) {
+                avio_wb16(pb, track->par->channels);
+                avio_wb16(pb, av_get_bytes_per_sample(track->par->format) * 8);
+            } else {
+                avio_wb16(pb, 2);
+                avio_wb16(pb, 16);
+            }
             avio_wb16(pb, 0);
         }
 
@@ -1009,6 +1035,8 @@ static int mov_write_audio_tag(AVFormatContext *s, AVIOContext *pb, MOVMuxContex
         mov_write_extradata_tag(pb, track);
     else if (track->par->codec_id == AV_CODEC_ID_WMAPRO)
         mov_write_wfex_tag(s, pb, track);
+    else if (track->par->codec_id == AV_CODEC_ID_FLAC)
+        mov_write_dfla_tag(pb, track);
     else if (track->vos_len > 0)
         mov_write_glbl_tag(pb, track);
 
@@ -1177,6 +1205,7 @@ static int mp4_get_codec_tag(AVFormatContext *s, MOVTrack *track)
     else if (track->par->codec_id == AV_CODEC_ID_DIRAC)     tag = MKTAG('d','r','a','c');
     else if (track->par->codec_id == AV_CODEC_ID_MOV_TEXT)  tag = MKTAG('t','x','3','g');
     else if (track->par->codec_id == AV_CODEC_ID_VC1)       tag = MKTAG('v','c','-','1');
+    else if (track->par->codec_id == AV_CODEC_ID_FLAC)      tag = MKTAG('f','L','a','C');
     else if (track->par->codec_type == AVMEDIA_TYPE_VIDEO)  tag = MKTAG('m','p','4','v');
     else if (track->par->codec_type == AVMEDIA_TYPE_AUDIO)  tag = MKTAG('m','p','4','a');
     else if (track->par->codec_id == AV_CODEC_ID_DVD_SUBTITLE)  tag = MKTAG('m','p','4','s');
@@ -5733,6 +5762,16 @@ static int mov_init(AVFormatContext *s)
                            i, track->par->sample_rate);
                 }
             }
+            if (track->mode == MODE_MP4 &&
+                track->par->codec_id == AV_CODEC_ID_FLAC) {
+                if (s->strict_std_compliance > FF_COMPLIANCE_EXPERIMENTAL) {
+                    av_log(s, AV_LOG_ERROR,
+                           "FLAC in MP4 support is experimental, add "
+                           "'-strict %d' if you want to use it.\n",
+                           FF_COMPLIANCE_EXPERIMENTAL);
+                    return AVERROR_EXPERIMENTAL;
+                }
+            }
         } else if (st->codecpar->codec_type == AVMEDIA_TYPE_SUBTITLE) {
             track->timescale = st->time_base.den;
         } else if (st->codecpar->codec_type == AVMEDIA_TYPE_DATA) {
-- 
2.10.1