demux: mp4: add basic WebVTT support

NEWS

@@ -120,8 +120,7 @@ Demuxers:
  * Support raw h265/hevc files
  * Support multi-channel WAV without channel-maps
  * Rewrite MKV seeking
- * Rewrite of TTML demuxer
- * Support for TTML in ISOBMF/MP4 and DASH
+ * Support for TTML and WebVTT in ISOBMF/MP4 and DASH
  * Fix Quicktime Mp4 inside MKV and unpacketized VC1
 
 Stream filter:

modules/demux/mp4/essetup.c

@@ -1177,7 +1177,10 @@ int SetupSpuES( demux_t *p_demux, mp4_track_t *p_track, MP4_Box_t *p_sample )
         case VLC_FOURCC('s','t','p','p'):
             p_track->fmt.i_codec = VLC_CODEC_TTML;
             break;
-
+        case ATOM_wvtt:
+            p_track->fmt.i_codec = VLC_CODEC_SUBT;
+            p_track->fmt.i_original_fourcc = ATOM_wvtt;
+            break;
         case ATOM_c608: /* EIA608 closed captions */
         //case ATOM_c708: /* EIA708 closed captions */
             p_track->fmt.i_codec = VLC_CODEC_EIA608_1;

modules/demux/mp4/libmp4.c

@@ -4257,6 +4257,9 @@ static const struct
     { ATOM_tx3g,    MP4_ReadBox_sample_tx3g,      0 },
     { ATOM_c608,    MP4_ReadBox_sample_clcp,      ATOM_stsd },
     //{ ATOM_text,    MP4_ReadBox_sample_text,    0 },
+    /* In sample WebVTT subtitle atoms. No ATOM_wvtt in normal parsing */
+    { ATOM_vttc,    MP4_ReadBoxContainer,         ATOM_wvtt },
+    { ATOM_payl,    MP4_ReadBox_Binary,           ATOM_vttc },
 
     /* for codecs */
     { ATOM_soun,    MP4_ReadBox_sample_soun,  ATOM_stsd },

modules/demux/mp4/libmp4.h

@@ -288,6 +288,11 @@ typedef int64_t stime_t;
 #define ATOM_clcp VLC_FOURCC( 'c', 'l', 'c', 'p' )
 #define ATOM_c608 VLC_FOURCC( 'c', '6', '0', '8' )
 #define ATOM_c708 VLC_FOURCC( 'c', '7', '0', '8' )
+#define ATOM_wvtt VLC_FOURCC( 'w', 'v', 't', 't' )
+
+/* In sample for WebVTT */
+#define ATOM_vttc VLC_FOURCC( 'v', 't', 't', 'c' )
+#define ATOM_payl VLC_FOURCC( 'p', 'a', 'y', 'l' )
 
 #define ATOM_0xa9nam VLC_FOURCC( 0xa9, 'n', 'a', 'm' )
 #define ATOM_0xa9aut VLC_FOURCC( 0xa9, 'a', 'u', 't' )

modules/demux/mp4/mp4.c

@@ -380,6 +380,38 @@ static int AllocateTracks( demux_t *p_demux, unsigned i_tracks )
     return VLC_SUCCESS;
 }
 
+static block_t * MP4_WebVTT_Convert( demux_t *p_demux, block_t * p_block )
+{
+    stream_t *p_stream =
+            vlc_stream_MemoryNew( p_demux, p_block->p_buffer,
+                                  p_block->i_buffer, true );
+    if( p_stream )
+    {
+        MP4_Box_t *p_vroot = MP4_BoxNew(ATOM_wvtt);
+        if( p_vroot )
+        {
+            p_vroot->i_size = p_block->i_buffer;
+            if ( MP4_ReadBoxContainerChildren( p_stream, p_vroot, NULL ) == 1 )
+            {
+                MP4_Box_t *p_payl = MP4_BoxGet( p_vroot, "vttc/payl" );
+                if( p_payl && p_payl->i_size >= 9 )
+                {
+                    p_block->p_buffer += p_payl->i_pos + 8;
+                    p_block->i_buffer = p_payl->i_size - 8;
+                    p_block->p_buffer[p_block->i_buffer - 1] = '\0';
+                }
+                else p_block->i_buffer = 0;
+#ifndef NDEBUG
+                MP4_BoxDumpStructure(p_stream, p_vroot);
+#endif
+            }
+            MP4_BoxFree(p_vroot);
+        }
+        vlc_stream_Delete( p_stream );
+     }
+    return p_block;
+}
+
 static block_t * MP4_EIA608_Convert( block_t * p_block )
 {
     /* Rebuild codec data from encap */
@@ -527,6 +559,10 @@ static block_t * MP4_Block_Convert( demux_t *p_demux, const mp4_track_t *p_track
             case VLC_CODEC_EIA608_1:
                 p_block = MP4_EIA608_Convert( p_block );
             break;
+            case VLC_CODEC_SUBT:
+                if( p_track->fmt.i_original_fourcc == ATOM_wvtt )
+                    p_block = MP4_WebVTT_Convert( p_demux, p_block );
+            break;
         default:
             p_block->i_buffer = 0;
             break;