mpegts-empty-ac3.patch

From e91022c98a8b48791d06f2e6c8d30125447e01f8 Mon Sep 17 00:00:00 2001
From: Aman Gupta <aman@tmm1.net>
Date: Tue, 19 Mar 2019 15:32:52 -0700
Subject: [PATCH] ffmpeg: skip automatic audio stream selection for missing ac3
 audio streams

Some mpegts samples will define an ac3 stream in the PAT for which audio data never appears:

  Program 3
    Stream #0:0[0x1a58]: Video: mpeg2video (Main) ([2][0][0][0] / 0x0002), yuv420p(tv, top first), 1920x1080 [SAR 1:1 DAR 16:9], Closed Captions, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc
    Stream #0:1[0x1a59](eng): Audio: ac3 ([129][0][0][0] / 0x0081), 48000 Hz, stereo, fltp, 384 kb/s
    Stream #0:2[0x1a4a](eng): Audio: ac3 ([129][0][0][0] / 0x0081), 0 channels, fltp

  Program 421
    Stream #0:0[0x621]: Video: mpeg2video (Main) ([2][0][0][0] / 0x0002), yuv420p(tv, bt709, top first), 1920x1080 [SAR 1:1 DAR 16:9], Closed Captions, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc
    Stream #0:1[0x623](eng): Audio: ac3 ([129][0][0][0] / 0x0081), 48000 Hz, 5.1(side), fltp, 384 kb/s
    Stream #0:2[0x622](eng): Audio: ac3 ([129][0][0][0] / 0x0081), 0 channels, fltp

When using `ffmpeg -i ... -map 0:a` to select all audio streams, these get selected and then ffmpeg fails because it cannot decode them.

Signed-off-by: Aman Gupta <aman@tmm1.net>
---
 fftools/ffmpeg_opt.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
index 262ee2b0ce..89285ce2b6 100644
--- a/fftools/ffmpeg_opt.c
+++ b/fftools/ffmpeg_opt.c
@@ -344,6 +344,7 @@ static int opt_map(void *optctx, const char *opt, const char *arg)
             }
         else
             for (i = 0; i < input_files[file_idx]->nb_streams; i++) {
+                AVCodecContext *dec_ctx = input_streams[input_files[file_idx]->ist_index + i]->dec_ctx;
                 if (check_stream_specifier(input_files[file_idx]->ctx, input_files[file_idx]->ctx->streams[i],
                             *p == ':' ? p + 1 : p) <= 0)
                     continue;
@@ -351,6 +352,13 @@ static int opt_map(void *optctx, const char *opt, const char *arg)
                     disabled = 1;
                     continue;
                 }
+                if (*p == ':' && *(p+1) == 'a' &&
+                    dec_ctx->codec_type == AVMEDIA_TYPE_AUDIO &&
+                    dec_ctx->codec_id == AV_CODEC_ID_AC3 &&
+                    dec_ctx->sample_rate == 0) {
+                    /* don't auto-select ac3 audio streams that failed probing */
+                    continue;
+                }
                 GROW_ARRAY(o->stream_maps, o->nb_stream_maps);
                 m = &o->stream_maps[o->nb_stream_maps - 1];