[FFmpeg-devel] [PATCH 1/2] avformat/mvdec: make audio stream conditional

[John-Paul Stewart <jpstewart-at-personalprojects.net@ffmpeg.org>]

Only allocate an audio stream if there is one in the data.  Silicon
Graphics movie format will contain default values (16 bit samples, 2
audio channels, 22050 Hz sample rate) even when no audio is present in
the file.  This confuses FFmpeg into thinking such an audio stream is
present with 0 samples in it.

There is a flag value in the format to indicate whether or not audio is
present.  This patch checks that and behaves accordingly.

Signed-off-by: John-Paul Stewart <jpstewart@personalprojects.net>
---
 libavformat/mvdec.c | 33 ++++++++++++++++++++++++---------
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/libavformat/mvdec.c b/libavformat/mvdec.c
index ea955d2b11..7493bcc762 100644
--- a/libavformat/mvdec.c
+++ b/libavformat/mvdec.c
@@ -45,6 +45,10 @@ typedef struct MvContext {
     int aformat;          ///< audio format
 } MvContext;
 
+/* these magic numbers are defined in moviefile.h on Silicon Grahpics IRIX */
+#define MOVIE_SOUND  1
+#define MOVIE_SILENT 2
+
 #define AUDIO_FORMAT_SIGNED 401
 
 static int mv_probe(const AVProbeData *p)
@@ -305,20 +309,27 @@ static int mv_read_header(AVFormatContext *avctx)
 
         avio_skip(pb, 10);
 
-        /* allocate audio track first to prevent unnecessary seeking
-         * (audio packet always precede video packet for a given frame) */
-        ast = avformat_new_stream(avctx, NULL);
-        if (!ast)
-            return AVERROR(ENOMEM);
-
         vst = avformat_new_stream(avctx, NULL);
         if (!vst)
             return AVERROR(ENOMEM);
         fps = av_d2q(av_int2double(avio_rb64(pb)), INT_MAX);
         avpriv_set_pts_info(vst, 64, fps.den, fps.num);
-        avio_skip(pb, 4);
         vst->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
         vst->avg_frame_rate = fps;
+
+        v = avio_rb16(pb);
+        if (v == MOVIE_SOUND) {
+            /* movie has sound, so allocate an audio stream */
+            ast = avformat_new_stream(avctx, NULL);
+            if (!ast)
+                return AVERROR(ENOMEM);
+
+            ast->codecpar->codec_type = AVMEDIA_TYPE_AUDIO;
+        } else if (v != MOVIE_SILENT)
+            return AVERROR_INVALIDDATA;
+
+        avio_skip(pb, 2);
+
         vst->duration = vst->nb_frames = avio_rb32(pb);
         v = avio_rb32(pb);
         switch (v) {
@@ -338,7 +349,7 @@ static int mv_read_header(AVFormatContext *avctx)
         vst->codecpar->height    = avio_rb32(pb);
         avio_skip(pb, 12);
 
-        ast->codecpar->codec_type  = AVMEDIA_TYPE_AUDIO;
+        if (ast) {
         ast->nb_frames          = vst->nb_frames;
         ast->codecpar->sample_rate = avio_rb32(pb);
         if (ast->codecpar->sample_rate <= 0) {
@@ -373,6 +384,8 @@ static int mv_read_header(AVFormatContext *avctx)
             return AVERROR_INVALIDDATA;
 
         avio_skip(pb, 8);
+        } else
+            avio_skip(pb, 24); /* skip meaningless audio metadata */
 
         var_read_metadata(avctx, "title", 0x80);
         var_read_metadata(avctx, "comment", 0x100);
@@ -386,9 +399,11 @@ static int mv_read_header(AVFormatContext *avctx)
             if (avio_feof(pb))
                 return AVERROR_INVALIDDATA;
             avio_skip(pb, 8);
+            if (ast) {
             av_add_index_entry(ast, pos, timestamp, asize, 0, AVINDEX_KEYFRAME);
-            av_add_index_entry(vst, pos + asize, i, vsize, 0, AVINDEX_KEYFRAME);
             timestamp += asize / (ast->codecpar->channels * (uint64_t)bytes_per_sample);
+            }
+            av_add_index_entry(vst, pos + asize, i, vsize, 0, AVINDEX_KEYFRAME);
         }
     } else if (!version && avio_rb16(pb) == 3) {
         avio_skip(pb, 4);
-- 
2.34.1

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