Cannot Play Video Output of Libavcodec (ffmpeg) Encoding Example

问题

From FFMPEG's GitHub, I use the encode_video.c to generate a 1 second video. Here is the example in question: https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/encode_video.c

I compile with: gcc -Wall -o ffencode encode_video.c -lavcodec -lavutil -lz -lm

Clean compile, zero warnings.

I test the program by running: ./ffencode video.mp4 libx264

Lots of stats printed out (expected based on source code) as well as ffmpeg logs, but ultimately no errors or warnings.

However, then the generated output video.mp4, can only be played by ffplay, and VLC Player (as well as Google Chrome) fail to play the video.

Playing it via vlc command line actually prints:

[00007ffd3550fec0] main libvlc: Running vlc with the default interface. Use 'cvlc' to use vlc without interface.
TagLib: MP4: Invalid atom size
TagLib: MP4: Invalid atom size
TagLib: MP4: Invalid atom size

Looking at ffprobe output, the bitrate and duration fields are empty:

Input #0, h264, from 'video.mp4':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: h264 (High), yuv420p(progressive), 352x288, 25 fps, 25 tbr, 1200k tbn, 50 tbc

I am using ffmpeg 4.1 with the following configuration:

ffprobe version 4.1 Copyright (c) 2007-2018 the FFmpeg developers
  built with Apple LLVM version 10.0.0 (clang-1000.11.45.5)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.1 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gpl --enable-libmp3lame --enable-libopus --enable-libsnappy --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-opencl --enable-videotoolbox
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100

Any ideas how to fix this? It is pretty surprising to see an API's official example to be lacking such basic information.

回答1:

You will need to perform muxing of your video stream into video container, such as .mp4. Muxing stuff is kept in libavformat. Algorithm should go like this:

Initialize format library by invoking av_register_all or manually registering formats of interests.
Create muxing context by invoking avformat_alloc_context
Create one or more media streams by invoking avformat_new_stream
Write header by invoking avformat_write_header
Write media data by invoking av_write_frame
Write trailer by invoking av_write_trailer
Destroy muxing context by invoking avformat_free_context

回答2:

The example generates a raw bitstream - it is not a MP4. The example is only meant to demonstrate encoding, not muxing (the term for packaging one or more streams into a container file format like MP4).

Rename extension to .h264 and test with VLC. No idea if Chrome supports raw .h264 files.

To generate MP4 from this output, run

ffmpeg -i video.mp4 -c copy actually.mp4

回答3:

can only be played by ffplay, and VLC Player (as well as Google Chrome) fail to play the video. Since ffplay is able to play the video, other media players can play it. You need to configure vlc to read X264 encoded video. Go to preference select all and change the demuxer to video H264

来源：https://stackoverflow.com/questions/53328946/cannot-play-video-output-of-libavcodec-ffmpeg-encoding-example

标签

video

ffmpeg

video-encoding

libavcodec