[FFmpeg-user] buffer underflow - processing VOB files

[Bob DeCarlo]

>Please share patch and input files.
Thanks Paul...
I generated the patch using git diff, this is not my code- just trying to be clear.  I found that the core dump was solved by this code change which allowed me to locate the code change that causes my buffer underrun problem.  Below are the contents of the patch.  

(  I cannot seem to access upload.ffmpeg.org, maybe my company firewall is blocking.  I will try again later.)

$ git diff 91bb871376730a2394ed0ae1a3fd4295977002d3
> 0b86ea03d8415b5a3a6b07f3012a8097bca26ea5 >p.patch

# This fixes the core dump issue, not the underrrun issue
$ cat p.patch 
diff --git a/libavcodec/ac3.h b/libavcodec/ac3.h
index 5c9c37727e..f8f6a81f45 100644
--- a/libavcodec/ac3.h
+++ b/libavcodec/ac3.h
@@ -28,6 +28,7 @@
 #define AVCODEC_AC3_H
 
 #define AC3_MAX_CODED_FRAME_SIZE 3840 /* in bytes */
+#define EAC3_MAX_CHANNELS 16          /**< maximum number of channels in EAC3 */
 #define AC3_MAX_CHANNELS 7            /**< maximum number of channels, including coupling channel */
 #define CPL_CH 0                      /**< coupling channel index */
 
diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index ac5c6d636a..b14d2e74ac 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -1488,7 +1488,7 @@ static int ac3_decode_frame(AVCodecContext * avctx, void *data,
     int blk, ch, err, offset, ret;
     int got_independent_frame = 0;
     const uint8_t *channel_map;
-    uint8_t extended_channel_map[AC3_MAX_CHANNELS * 2];
+    uint8_t extended_channel_map[EAC3_MAX_CHANNELS];
     const SHORTFLOAT *output[AC3_MAX_CHANNELS];
     enum AVMatrixEncoding matrix_encoding;
     AVDownmixInfo *downmix_info;
@@ -1685,7 +1685,7 @@ dependent_frame:
         avctx->bit_rate    = s->bit_rate + s->prev_bit_rate;
     }
 
-    for (ch = 0; ch < 16; ch++)
+    for (ch = 0; ch < EAC3_MAX_CHANNELS; ch++)
         extended_channel_map[ch] = ch;
 
     if (s->frame_type == EAC3_FRAME_TYPE_DEPENDENT) {
@@ -1698,7 +1698,7 @@ dependent_frame:
 
         channel_layout = ich_layout;
         for (ch = 0; ch < 16; ch++) {
-            if (s->channel_map & (1 << (15 - ch))) {
+            if (s->channel_map & (1 << (EAC3_MAX_CHANNELS - ch - 1))) {
                 channel_layout |= custom_channel_map_locations[ch][1];
             }
         }
@@ -1706,8 +1706,8 @@ dependent_frame:
         avctx->channel_layout = channel_layout;
         avctx->channels = av_get_channel_layout_nb_channels(channel_layout);
 
-        for (ch = 0; ch < 16; ch++) {
-            if (s->channel_map & (1 << (15 - ch))) {
+        for (ch = 0; ch < EAC3_MAX_CHANNELS; ch++) {
+            if (s->channel_map & (1 << (EAC3_MAX_CHANNELS - ch - 1))) {
                 if (custom_channel_map_locations[ch][0]) {
                     int index = av_get_channel_layout_channel_index(channel_layout,
                                                                     custom_channel_map_locations[ch][1]);
diff --git a/libavcodec/ac3dec.h b/libavcodec/ac3dec.h
index ae5ef4bbc9..ce1434b55c 100644
--- a/libavcodec/ac3dec.h
+++ b/libavcodec/ac3dec.h
@@ -242,12 +242,12 @@ typedef struct AC3DecodeContext {
 ///@name Aligned arrays
     DECLARE_ALIGNED(16, int,   fixed_coeffs)[AC3_MAX_CHANNELS][AC3_MAX_COEFS];       ///< fixed-point transform coefficients
     DECLARE_ALIGNED(32, INTFLOAT, transform_coeffs)[AC3_MAX_CHANNELS][AC3_MAX_COEFS];   ///< transform coefficients
-    DECLARE_ALIGNED(32, INTFLOAT, delay)[2 * AC3_MAX_CHANNELS][AC3_BLOCK_SIZE];         ///< delay - added to the next block
+    DECLARE_ALIGNED(32, INTFLOAT, delay)[EAC3_MAX_CHANNELS][AC3_BLOCK_SIZE];         ///< delay - added to the next block
     DECLARE_ALIGNED(32, INTFLOAT, window)[AC3_BLOCK_SIZE];                              ///< window coefficients
     DECLARE_ALIGNED(32, INTFLOAT, tmp_output)[AC3_BLOCK_SIZE];                          ///< temporary storage for output before windowing
-    DECLARE_ALIGNED(32, SHORTFLOAT, output)[2 * AC3_MAX_CHANNELS][AC3_BLOCK_SIZE];            ///< output after imdct transform and windowing
+    DECLARE_ALIGNED(32, SHORTFLOAT, output)[EAC3_MAX_CHANNELS][AC3_BLOCK_SIZE];            ///< output after imdct transform and windowing
     DECLARE_ALIGNED(32, uint8_t, input_buffer)[AC3_FRAME_BUFFER_SIZE + AV_INPUT_BUFFER_PADDING_SIZE]; ///< temp buffer to prevent overread
-    DECLARE_ALIGNED(32, SHORTFLOAT, output_buffer)[2 * AC3_MAX_CHANNELS][AC3_BLOCK_SIZE * 6];  ///< final output buffer
+    DECLARE_ALIGNED(32, SHORTFLOAT, output_buffer)[EAC3_MAX_CHANNELS][AC3_BLOCK_SIZE * 6];  ///< final output buffer
 ///@}
 } AC3DecodeContext;

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