[FFmpeg-devel] [PATCH] avcodec/mp3: fix skipping zeros

wm4 nfxjfg at googlemail.com
Wed Sep 30 14:54:11 CEST 2015

Commits 43bc5cf9 and c5371f77 add code for skipping initial zeros in mp3
packets. (There are no explanations, no samples.)

This code forgot to report to the user that data was skipped at all. IT
should do this by adding the skipped amount of bytes to the amount of
consumed bytes returned by the decode call.

Since audio codecs allow partial packet decoding, the user application
has to rely on the return value. It will remove the data reported as
consumed by the decoder, and feed it to the decoder again. This resulted
in the mp3 frame after the zero region to be decoded over and over
again, until the zero region was finally skipped by the application.

Fixes trac ticket #4890.
 libavcodec/mpegaudiodec_template.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libavcodec/mpegaudiodec_template.c b/libavcodec/mpegaudiodec_template.c
index b7b9dbd..0f32ac7 100644
--- a/libavcodec/mpegaudiodec_template.c
+++ b/libavcodec/mpegaudiodec_template.c
@@ -1657,9 +1657,11 @@ static int decode_frame(AVCodecContext * avctx, void *data, int *got_frame_ptr,
     uint32_t header;
     int ret;
+    int skipped = 0;
     while(buf_size && !*buf){
+        skipped++;
     if (buf_size < HEADER_SIZE)
@@ -1714,7 +1716,7 @@ static int decode_frame(AVCodecContext * avctx, void *data, int *got_frame_ptr,
             return ret;
     s->frame_size = 0;
-    return buf_size;
+    return buf_size + skipped;
 static void mp_flush(MPADecodeContext *ctx)

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