轉自：https://stackoverflow.com/questions/42220081/how-to-choose-between-openh264-and-x264-decoder

avcodec_find_decoder(AVCodecID.AV_CODEC_ID_H264); 

codec = avcodec_find_decoder _by_name("x264");
codec = avcodec_find_decoder _by_name("libx264");

FFmpeg can use OpenH264 (named libopenh264 in FFmpeg) to decode in addition to the native FFmpeg H.264 decoder (named h264). There are also several supported hardware assisted H.264 decoders

Caveats

• OpenH264 can only decode Constrained Baseline profile, so its usefulness may be limited.

• The native FFmpeg H.264 decoder has threading capabilities (frame and slice) but OpenH264 does not.

ffmpeg CLI tool examples

It appears you're working with the FFmpeg libraries, but here are some examples using ffmpeg.

To choose the decoder you want use the -c:v input option. Below are two decoding benchmark examples using the null muxer. The -map option is also used so only the (first) video stream is decoded and to ignore other, non-video streams such as audio.

Native FFmpeg H.264 decoder

$ ffmpeg -benchmark -i input.mp4 -map 0:v:0 -f null -
bench: utime=23.557s
bench: maxrss=57752kB
real    0m3.834s
user    0m23.573s
sys     0m0.213s

libopenh264

$ ffmpeg -benchmark -c:v libopenh264 -i input.mp4 -map 0:v:0 -f null -
bench: utime=20.927s
bench: maxrss=37404kB
real    0m21.002s
user    0m20.940s
sys     0m0.060s

Benchmark time

Note the benchmark option outputs user CPU time, not the elapsed real time. If you want real time as well add the time command before the ffmpeg command (if you're on Linux). I added the outputs from time in the example (the last three lines) for comparison purposes.

To verify the desired decoder is being used

View the console output. For example using the native H.264 decoder:

Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> wrapped_avframe (native))

Using libopenh264:

Stream mapping:
  Stream #0:0 -> #0:0 (h264 (libopenh264) -> wrapped_avframe (native))

avcodec_find_decoder(AVCodecID.AV_CODEC_ID_H264); 

codec = avcodec_find_decoder _by_name("x264");
codec = avcodec_find_decoder _by_name("libx264");