Build failure with latest ffmpeg master caused by deprecated/removed attributes

[prabhat00155]

Building torchvision from source with latest ffmpeg(installed from source) throws a number of errors:

• pict attribute

/Users/prabhatroy/Documents/pytorch/repos/vision/torchvision/csrc/io/decoder/util.cpp:52:25: error: no member named 'pict' in 'AVSubtitleRect'
          s += sizeof(y.pict.linesize[i]);
                      ~ ^

The reason is that ffmpeg's AVSubtitleRect's pict attribute was deprecated in 3.0 and removed in the latest master.

• av_frame_get_best_effort_timestamp

/Users/prabhatroy/Documents/pytorch/repos/vision/torchvision/csrc/io/decoder/stream.cpp:235:19: error: use of undeclared identifier 'av_frame_get_best_effort_timestamp'
    header->pts = av_frame_get_best_effort_timestamp(frame_);
                  ^
1 error generated.

av_frame_get_best_effort_timestamp() was deprecated in ffmpeg 4.0 and removed from the latest master.

We need to update its usage in torchvision.

cc @bjuncek

[bjuncek]

In addition to above here are few other things to consider changing (this list will be updated)

High (build failures)

see above

Low (warnings and incorrect usage)

• av_register_all
• AVStream->codec is being depreciated

[bjuncek]

Since most of these have been closed I'm closing the issue.