I have an mp4 video (of a lecture) containing two streams, video and audio. I wanted an introduction for it (title slide of the presentation that accompanied it), so I made an mp4 out of the intro image via ffmpeg -framerate 30 -i lec01_title.jpg -t 3 -c:v libx264 -pix_fmt yuvj420p -vf "scale=1920:1080" lec01_title.mp4 -f lavfi -i anullsrc -c:a aac. When I try to concat the files using the demuxer, it doesn't work. First, I try to verify that the properties (encoding, etc.) of the two videos are the same.
If I run ffmpeg -i lec01.mp4, I get:
ffmpeg version 5.1.1 Copyright (c) 2000-2022 the FFmpeg developers
built with Apple clang version 12.0.0 (clang-1200.0.32.29)
configuration: --prefix=/usr/local/Cellar/ffmpeg/5.1.1 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
libavutil 57. 28.100 / 57. 28.100
libavcodec 59. 37.100 / 59. 37.100
libavformat 59. 27.100 / 59. 27.100
libavdevice 59. 7.100 / 59. 7.100
libavfilter 8. 44.100 / 8. 44.100
libswscale 6. 7.100 / 6. 7.100
libswresample 4. 7.100 / 4. 7.100
libpostproc 56. 6.100 / 56. 6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'dcai_lec01.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
title : Wide
encoder : Lavf58.20.100
Duration: 00:45:24.01, start: 0.000000, bitrate: 743 kb/s
Stream #0:0[0x1](und): Audio: aac (LC) (mp4a / 0x6134706D), 96000 Hz, stereo, fltp, 129 kb/s (default)
Metadata:
handler_name : SoundHandler
vendor_id : [0][0][0][0]
Stream #0:1[0x2](und): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 606 kb/s, 30 fps, 30 tbr, 15360 tbn (default)
Metadata:
handler_name : VideoHandler
vendor_id : [0][0][0][0]
If I run ffmpeg -i lec01_title.mp4, I get:
ffmpeg version 5.1.1 Copyright (c) 2000-2022 the FFmpeg developers
built with Apple clang version 12.0.0 (clang-1200.0.32.29)
configuration: --prefix=/usr/local/Cellar/ffmpeg/5.1.1 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
libavutil 57. 28.100 / 57. 28.100
libavcodec 59. 37.100 / 59. 37.100
libavformat 59. 27.100 / 59. 27.100
libavdevice 59. 7.100 / 59. 7.100
libavfilter 8. 44.100 / 8. 44.100
libswscale 6. 7.100 / 6. 7.100
libswresample 4. 7.100 / 4. 7.100
libpostproc 56. 6.100 / 56. 6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'dcai_lec01_title.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf59.27.100
Duration: 00:00:03.00, start: 0.000000, bitrate: 150 kb/s
Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc, bt470bg/unknown/unknown, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 12877 kb/s, 30 fps, 30 tbr, 15360 tbn (default)
Metadata:
handler_name : VideoHandler
vendor_id : [0][0][0][0]
encoder : Lavc59.37.100 libx264
Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 2 kb/s (default)
Metadata:
handler_name : SoundHandler
vendor_id : [0][0][0][0]
I tried to verify that the properties of the two videos match via ffprobe -select_streams a:0 -show_entries stream=codec_name,channels -of default=nw=1:nk=1 -v 0 lec01.mp4 and ffprobe -select_streams v:0 -show_entries stream=codec_name,width,height,r_frame_rate,pix_fmt -of default=nw=1:nk=1 -v 0 lec01.mp4, and they do. The first command gives me
aac
2
and the second command gives me
h264
1920
1080
yuvj420p
30/1
for both videos.
Now, if I have a file called lec01.txt containing:
file 'lec01_title.mp4'
file 'lec01.mp4'
when I run ffmpeg -f concat -i lec01.txt -c copy output.mp4, the resulting video is of length 04:44:04 (four hours, when my two input videos were 3 seconds and 45:24 minutes respectively), and it only shows the title slide for that entire duration.
Furthermore, when I run this concat command, I get the following message repeated many times: [mp4 @ 0x7f82b9013b80] Non-monotonous DTS in output stream 0:1; previous: 133290, current: 133120; changing to 133291. This may result in incorrect timestamps in the output file.
I'm missing something. When I look up this error, it seems to be something related to the decoding time stamps (DTS) or presentation time stamps. Anyone know what I'm doing wrong and how to fix? Thank you for your help!
Edit:
It appears to work if I re-encode via ffmpeg -i lec01_title.mp4 -i lec01.mp4 -filter_complex "[0:v:0][0:a:0][1:v:0][1:a:0]concat=n=2:v=1:a=1[outv][outa]" -map "[outv]" -map "[outa]" output.mp4, but I'd like to avoid doing this since I have tons of videos I need to do this for.
