[FFmpeg-devel] [PATCH v2] ffmpeg_opt: restore documented stream selection behaviour

[Gyan Doshi]

11d3b03fcb added consideration of default stream disposition for audio
and video when choosing the 'best' stream among all the inputs. This can
lead to video streams with lower resolution or audio streams with fewer
channels being selected.

Stream disposition, however, only sets a priority for a stream
among all other streams in the *same input*. It cannot set a priority
for a stream across all inputs.

This patch sets a middle-way and selects the best stream from each file
with default disposition considered. Then it discards disposition weight
and selects best stream as per the original criteria of highest
resolution for video and most channels for audio.
---

Corrected out-of-bounds input stream access.

 fftools/ffmpeg_opt.c | 78 +++++++++++++++++++++++++++++---------------
 1 file changed, 51 insertions(+), 27 deletions(-)

diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
index 1b43bab9fc..72eddf3678 100644
--- a/fftools/ffmpeg_opt.c
+++ b/fftools/ffmpeg_opt.c
@@ -2260,23 +2260,34 @@ static int open_output_file(OptionsContext *o, const char *filename)
         if (!o->video_disable && av_guess_codec(oc->oformat, NULL, filename, NULL, AVMEDIA_TYPE_VIDEO) != AV_CODEC_ID_NONE) {
             int best_score = 0, idx = -1;
             int qcr = avformat_query_codec(oc->oformat, oc->oformat->video_codec, 0);
-            for (i = 0; i < nb_input_streams; i++) {
-                int score;
-                ist = input_streams[i];
-                score = ist->st->codecpar->width * ist->st->codecpar->height
-                           + 100000000 * !!(ist->st->event_flags & AVSTREAM_EVENT_FLAG_NEW_PACKETS)
-                           + 5000000*!!(ist->st->disposition & AV_DISPOSITION_DEFAULT);
-                if (ist->user_set_discard == AVDISCARD_ALL)
-                    continue;
-                if((qcr!=MKTAG('A', 'P', 'I', 'C')) && (ist->st->disposition & AV_DISPOSITION_ATTACHED_PIC))
-                    score = 1;
-                if (ist->st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
-                    score > best_score) {
-                    if((qcr==MKTAG('A', 'P', 'I', 'C')) && !(ist->st->disposition & AV_DISPOSITION_ATTACHED_PIC))
+            for (j = 0; j < nb_input_files; j++) {
+                InputFile *ifile = input_files[j];
+                int file_best_score = 0, file_best_idx = -1;
+                for (i = 0; i < ifile->nb_streams; i++) {
+                    int score;
+                    ist = input_streams[ifile->ist_index + i];
+                    score = ist->st->codecpar->width * ist->st->codecpar->height
+                               + 100000000 * !!(ist->st->event_flags & AVSTREAM_EVENT_FLAG_NEW_PACKETS)
+                               + 5000000*!!(ist->st->disposition & AV_DISPOSITION_DEFAULT);
+                    if (ist->user_set_discard == AVDISCARD_ALL)
                         continue;
-                    best_score = score;
-                    idx = i;
+                    if((qcr!=MKTAG('A', 'P', 'I', 'C')) && (ist->st->disposition & AV_DISPOSITION_ATTACHED_PIC))
+                        score = 1;
+                    if (ist->st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&
+                        score > file_best_score) {
+                        if((qcr==MKTAG('A', 'P', 'I', 'C')) && !(ist->st->disposition & AV_DISPOSITION_ATTACHED_PIC))
+                            continue;
+                        file_best_score = score;
+                        file_best_idx = ifile->ist_index + i;
+                    }
                 }
+                if (file_best_idx >= 0) {
+                    file_best_score -= 5000000*!!(input_streams[file_best_idx]->st->disposition & AV_DISPOSITION_DEFAULT);
+                    if (file_best_score > best_score) {
+                        best_score = file_best_score;
+                        idx = file_best_idx;
+                    }
+               }
             }
             if (idx >= 0)
                 new_video_stream(o, oc, idx);
@@ -2285,19 +2296,32 @@ static int open_output_file(OptionsContext *o, const char *filename)
         /* audio: most channels */
         if (!o->audio_disable && av_guess_codec(oc->oformat, NULL, filename, NULL, AVMEDIA_TYPE_AUDIO) != AV_CODEC_ID_NONE) {
             int best_score = 0, idx = -1;
-            for (i = 0; i < nb_input_streams; i++) {
-                int score;
-                ist = input_streams[i];
-                score = ist->st->codecpar->channels
-                        + 100000000 * !!(ist->st->event_flags & AVSTREAM_EVENT_FLAG_NEW_PACKETS)
-                        + 5000000*!!(ist->st->disposition & AV_DISPOSITION_DEFAULT);
-                if (ist->user_set_discard == AVDISCARD_ALL)
-                    continue;
-                if (ist->st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO &&
-                    score > best_score) {
-                    best_score = score;
-                    idx = i;
+            for (j = 0; j < nb_input_files; j++) {
+                InputFile *ifile = input_files[j];
+                int file_best_score = 0, file_best_idx = -1;
+                for (i = 0; i < ifile->nb_streams; i++) {
+                    int score;
+                    ist = input_streams[ifile->ist_index + i];
+                    score = ist->st->codecpar->channels
+                            + 100000000 * !!(ist->st->event_flags & AVSTREAM_EVENT_FLAG_NEW_PACKETS)
+                            + 5000000*!!(ist->st->disposition & AV_DISPOSITION_DEFAULT);
+av_log(NULL, AV_LOG_WARNING, "within file %d istindex %d i %d score %d file_best_score %d file_best_idx %d best_score %d idx %d\n",
+       j, ifile->ist_index, i, score, file_best_score, file_best_idx, best_score, idx);
+                    if (ist->user_set_discard == AVDISCARD_ALL)
+                        continue;
+                    if (ist->st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO &&
+                        score > file_best_score) {
+                        file_best_score = score;
+                        file_best_idx = ifile->ist_index + i;
+                    }
                 }
+                if (file_best_idx >= 0) {
+                    file_best_score -= 5000000*!!(input_streams[file_best_idx]->st->disposition & AV_DISPOSITION_DEFAULT);
+                    if (file_best_score > best_score) {
+                        best_score = file_best_score;
+                        idx = file_best_idx;
+                    }
+               }
             }
             if (idx >= 0)
                 new_audio_stream(o, oc, idx);
-- 
2.32.0