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• vf_psnr : add channel weighting based on chroma subsampling.

  11 juillet 2015, par Ronald S. Bultje

  vf_psnr : add channel weighting based on chroma subsampling.
  Also add per-channel psnr stream averages to final log message.
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavfilter/vf_psnr.c

• Static image and a folder of mp3's ?

  28 juin 2013, par Shirohige

  I want to create a bunch of videos consisting of an single image which is shown throughout the whole video but each video has a different audio file. I can do it manually with various tools but the problem is that I have a lot of audio files and I can't optimize the frame rate (more on that later) and it takes a lot of time to do it that way but ffmpeg offers everything I need but the problem is that I don't know how to batch process everything.

  The basic code :
  ffmpeg -i song-name.mp3 -loop 1 -i cover.jpg -r frame-rate -t song-length -acodec copy output.mp4

  What I want to achieve :
  Let's say that I have a folder which consists of several audio files : song-name-1.mp3, song-name-2.mp3, ..., song-name-n.mp3 and cover.jpg.

  I need a batch file which takes the name of every mp3 file in a folder (a FOR loop I suppose) and processes it with the same command :
  ffmpeg -i song-name.mp3 -loop 1 -i cover.jpg -r frame-rate -t song-length -acodec copy output.mp4

  So the image is always the same for every video. The song length can be taken with the tool mp3info and the corresponding command :
  mp3info.exe -p %S song-name.mp3

  Since I only have one image throughout the whole video, the optimal frame rate would be the inverse of the video length which is 1/length (where length is a variable in seconds which we get from mp3info).

  So the final code should look something like this :
  ffmpeg -i song-name.mp3 -loop 1 -i cover.jpg -r 1/length -t length -acodec copy song-name.mp4

  Where "song-name" is a variable which changes for every iteration of the FOR loop (i.e. for every audio file in the folder) and length is a variable whose value we get with the command :
  mp3info.exe -p %S song-name.mp3

  I found examples of a FOR loop to fetch all file names of all mp3's in a specific folder but I do not know how to integrate mp3info. I hope that somebody can help me and I have some knowledge of the C programming language if that can be used in any way.

• Concatenate MOV files without re-encoding on iOS with ffmpeg libs

  2 juillet 2013, par Developer82

  I would like to concatenate MOV files without re-encoding. I want to do it on iOS (iPhone). All the MOV files are recorded with the same settings, no difference in dimensions or encoding profiles.

  I have succeeded to do it with the command line ffmpeg :
  ffmpeg -re -f concat -i files.txt -c copy ...
  But I have difficulties using the libraries.

  I think the demuxing part is ok, I have the h.264+AAC packets. After demuxing I shift the PTS and DTS info of each packet to have ascending values in the joined MOV file.
  The hard part is the muxing.

  I have built the ffmpeg libs with x264 lib, so it can be used if necessary, but I am not sure whether I need the x264 codec since I don't want to re-encode the MOV files, I just want to join them.

  Problems I have encountered :

  1. In this case I do not use x264 codec. At muxing I create the stream with NULL codec parameter. I have successful writing of header, packets and trailer. All the function calls return with zero error code. However, the output can be opened, but black "screen" is displayed during playback. FFprobe report is attached. I have also examined the output with MediaInfo tool. I have attached that report as well (MediaInfo report - without x264 codec.txt). As you can see there is no h.264 profile or pixel info found that might be a problem.

  2. In this case I use x264 codec with functions : avcodec_find_encoder, avformat_new_stream and avcodec_open2. Again : no decode-encode ! In this case I have much more metadata in the output file like h.264 profile and pixel info (YUV), but the av_interleaved_write_frame call simply does nothing but returns success code (0). No packet is written to the file. :( I don't know how this could happen. fwrite works, but results in un-openable file. I have also attached the MediaInfo report of this output (MediaInfo report - with x264 codec.txt).

  Questions :

  • How should I process the demuxed packets to feed the muxer ?
  • What format context and codec context setting should be done including AVOption settings ?
  • Should I use the x264 codec to do this ? I just vant to re-mux the chunks into a single joined file.
  • The chunks have their own header/trailer. Should I somehow filter the demuxed packets to skip them ?
  • The final goal is creating a network stream (RTP or RTMP) - also with re-muxing and without re-encoding. It works with command line ffmpeg :
    ffmpeg -re -f concat -i files.txt -vcodec copy -an -f rtp rtp://127.0.0.1:20000 -vn -acodec copy -f rtp rtp://127.0.0.1:30000

  Concatenating to MOV format is only an intermediate pilot. Is it recommended to work on the network format since it is so different task that there is no benefit of solving the MOV format muxing ?

  Any help, advice, suggestion is greatly appreciated.
  I can reveal code to make deeper investigation possible.

  Thanks !