[FFmpeg-user] Match audio and video duration during concat/encode

[Gian Maria Allibrante]

May I ask help to understand how to match audio and video duration during ffmpeg encoding for a concatenation of videos destined to an infinite loop mpeg dash transmission with closed GOP every two seconds (mp4box).

first step for audio encoding and timebase uniformity of each video before the concat/encode process:

ffmpeg -y -i "$f" -c copy -video_track_timescale 90k -c:a aac -b:a 384k -ar 44100 -ac 2 -shortest -af aresample=async=1 ../buffer/${NAME}_buffer.mp4

Then concat/encode process in order to get total duration in seconds multiple of closed GOP for example: cutting 373.5 duration to obtain 372.000 duration:

ffmpeg -f concat -safe 0 -y -i list.txt -loop 1 -i ../logo/logo.png -c:a copy -c:v libx264 -x264opts keyint=$GOP:min-keyint=$GOP:no-scenecut -bf 0 -r $FPSC -b:v 4800k -maxrate 9600k -bufsize 19200k -profile:v main -crf 22 -filter_complex "[0:v][1:v]overlay=main_w-overlay_w-10:10,scale=1920:1080,setsar=1" -t $TOTDUR 1080set.mp4

The result duration:

VIDEO FORMAT CONTAINER DURATION:
372.000000
VIDEO STREAM DURATION:
372.000000
AUDIO FORMAT CONTAINER DURATION:
372.006000

These are the videos that i used for test:
thanks in advance!
Jan

Metadata:
    major_brand     : isom
    minor_version   : 1
    compatible_brands: isomavc1
    creation_time   : 2007-05-09T07:55:25.000000Z
  Duration: 00:01:29.22, start: 0.000000, bitrate: 7490 kb/s
    Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 1920x816, 7403 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 47.95 tbc (default)
    Metadata:
      creation_time   : 2007-05-09T07:55:25.000000Z
      handler_name    : GPAC ISO Video Handler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 94 kb/s (default)
    Metadata:
      creation_time   : 2007-05-09T07:55:29.000000Z
      handler_name    : GPAC ISO Audio Handler

  Metadata:
    major_brand     : isom
    minor_version   : 1
    compatible_brands: isomavc1
    creation_time   : 2007-07-17T09:18:37.000000Z
    genre           : Trailer
    artist          : Fox
    title           : The Simpsons Movie
    date            : 2007
  Duration: 00:02:17.25, start: 0.000000, bitrate: 8591 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x800, 8486 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 47.95 tbc (default)
    Metadata:
      creation_time   : 2007-07-17T09:18:37.000000Z
      handler_name    : GPAC ISO Video Handler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, 5.1, fltp, 107 kb/s (default)
    Metadata:
      creation_time   : 2007-07-17T09:18:45.000000Z
      handler_name    : GPAC ISO Audio Handler
    Stream #0:2: Video: mjpeg (Progressive), yuvj420p(pc, bt470bg/unknown/unknown), 101x150 [SAR 72:72 DAR 101:150], 90k tbr, 90k tbn, 90k tbc (attached pic)

  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: mp42isomavc1
    creation_time   : 2013-12-01T03:59:56.000000Z
    genre           : Trailer
    artist          : Warner Bros.
    title           : Gravity - 2K Trailer
    encoder         : HandBrake 0.9.9 2013051800
    date            : 2013
  Duration: 00:02:27.07, start: 0.000000, bitrate: 20296 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 2048x858, 20149 kb/s, 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc (default)
    Metadata:
      creation_time   : 2013-12-01T03:59:56.000000Z
      encoder         : JVT/AVC Coding
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 153 kb/s (default)
    Metadata:
      creation_time   : 2013-12-01T03:59:56.000000Z
    Stream #0:2: Video: mjpeg (Baseline), yuvj420p(pc, bt470bg/unknown/unknown), 102x150 [SAR 72:72 DAR 17:25], 90k tbr, 90k tbn, 90k tbc (attached pic)