Title: Package my video Date: 2024-06-20T13:19:03-04:00 Draft: 1 --- ## TODO * Some intro * Investigate key frames and seeking -------------------------------------------------------------------------------- The goal of this project is to get a minimum viable product of: * support H264 video and AAC audio * experiment with AV1 and Opus if time permits * produce a .mp4 file that is optimized for: raw progressive playback and segment generation * generate a HLS playlist on demand * generate the Nth segment from a HLS file on demand ## Setup ### ffmpeg First I want to start with the latest available ffmpeg static build from: ```shell ❯ curl -sL -O https://johnvansickle.com/ffmpeg/releases/ffmpeg-release-amd64-static.tar.xz ❯ sudo tar -C /opt -xvf ffmpeg-release-amd64-static.tar.xz ``` My preference is to then link my preferred build to some location (`/opt/ffmpeg-static`) that I will then add to my `PATH`. ``` ❯ sudo ln -sf /opt/ffmpeg-7.0.1-amd64-static/ /opt/ffmpeg-static # then edit your shell rc or profile, reset shell ❯ type ffmpeg ffmpeg is /opt/ffmpeg-static/ffmpeg ❯ ffmpeg -version ffmpeg version 7.0.1-static https://johnvansickle.com/ffmpeg/ Copyright (c) 2000-2024 the FFmpeg developers built with gcc 8 (Debian 8.3.0-6) configuration: --enable-gpl --enable-version3 --enable-static --disable-debug --disable-ffplay --disable-indev=sndio --disable-outdev=sndio --cc=gcc --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gmp --enable-libgme --enable-gray --enable-libaom --enable-libfribidi --enable-libass --enable-libvmaf --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librubberband --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libvorbis --enable-libopus --enable-libtheora --enable-libvidstab --enable-libvo-amrwbenc --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libdav1d --enable-libxvid --enable-libzvbi --enable-libzimg libavutil 59. 8.100 / 59. 8.100 libavcodec 61. 3.100 / 61. 3.100 libavformat 61. 1.100 / 61. 1.100 libavdevice 61. 1.100 / 61. 1.100 libavfilter 10. 1.100 / 10. 1.100 libswscale 8. 1.100 / 8. 1.100 libswresample 5. 1.100 / 5. 1.100 libpostproc 58. 1.100 / 58. 1.100 ``` And checking codec support ``` ❯ ffmpeg -codecs 2>/dev/null | grep '\s\(aac\|h264\|av1\|opus\)' DEV.L. av1 Alliance for Open Media AV1 (decoders: libdav1d libaom-av1 av1) (encoders: libaom-av1) DEV.LS h264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 (decoders: h264 h264_v4l2m2m) (encoders: libx264 libx264rgb h264_v4l2m2m) DEAIL. aac AAC (Advanced Audio Coding) (decoders: aac aac_fixed) D.AIL. aac_latm AAC LATM (Advanced Audio Coding LATM syntax) DEAIL. opus Opus (Opus Interactive Audio Codec) (decoders: opus libopus) (encoders: opus libopus) ``` ### Test video file Here are a few and open test video sources: * Sintel: * License: [Creative Commons Attribution 3.0](https://web.archive.org/web/20240105060647/https://durian.blender.org/sharing/) * Big Buck Bunny: * License: [Creative Commons Attribution 3.0](https://web.archive.org/web/20240521095028/https://peach.blender.org/about/) I grabbed a 720p version of each ```shell ❯ du -h test-videos/* 398M test-videos/big_buck_bunny_720p_h264.mov 650M test-videos/Sintel.2010.720p.mkv ``` ### Deciding on eventual segment size Target segment size will hold some influence over our progressive transcoding. Each segment will begin with at least 1 key frame, so our progressive output key frame placement should line up with where our segments will be extracted. Apple [suggests 6 second durations for each HLS segment][apple_hls_seg] for VOD playback with HLS. 6s would be fine to use, but it's a choice with consequences. If there was a desire to use a 3s segment instead, the progressive file would need to re-transcode to insert more key frames. So for flexibility's sake will choose 3s for key frames in the progressive transcode, but eventual segments will be 6s. ### Packaging the progressive file But first, let's produce v1 of the files with the target codecs applied (H264 and AAC). ``` ❯ ffmpeg -i ./test-videos/big_buck_bunny_720p_h264.mov -acodec 'aac' -vcodec 'h264' ./test-videos/bbb_h264_aac.mp4 ❯ ffmpeg -i ./test-videos/Sintel.2010.720p.mkv -acodec 'aac' -vcodec 'h264' ./test-videos/sintel_h264_aac.mp4 ❯ du -h ./test-videos/* 138M ./test-videos/bbb_h264_aac.mp4 398M ./test-videos/big_buck_bunny_720p_h264.mov 650M ./test-videos/Sintel.2010.720p.mkv 201M ./test-videos/sintel_h264_aac.mp4 ``` Now lets inspect the frames a bit closer with this script `dumpframes.sh` ```bash #!/usr/bin/env bash ffprobe -select_streams v -show_frames -show_entries frame=pict_type -of csv $1 ``` This should show what [picture type][pic_types] each frame is. > I‑frames are the least compressible but don't require other video frames to decode. > P‑frames can use data from previous frames to decompress and are more compressible than I‑frames. > B‑frames can use both previous and forward frames for data reference to get the highest amount of data compression. **I** frames are also called **key frames**. So given a dump of Big Buck Bunny (BBB): ``` ./dumpframes.sh test-videos/bbb_h264_aac.mp4 > bbb_frames.csv ``` BBB is 24fps, so every 3 seconds we want to see a key frame. Here are the frame numbers where the key frame should be. ``` ❯ python3 >>> fps = 24 >>> i_frame_s = 3 >>> for i in range(0, 10): print(i * fps * i_frame_s + 1) ... 1 73 145 217 289 361 433 505 577 649 ``` * First segment should contain 3s of content which will be 72 frames. * First frame should be a key frame. * Then 71 non I frames. * Then the next I frame (frame 73) begins the next segment. But our frames are not quite right. ```shell ❯ grep -n I ./bbb_frames.csv | head 1:frame,I,H.26[45] User Data Unregistered SEI message 7:frame,I 251:frame,I 286:frame,I 379:frame,I 554:frame,I 804:frame,I 1054:frame,I 1146:frame,I 1347:frame,I ``` This is because we didn't tell ffmpeg anything about how to encode and where to place I frames. There are a few options to `libx264` that help control this: * `--no-scenecut`: "Disable adaptive I-frame decision" * `--keyint`: effectively the key frame interval. Technically it is the "Maximum GOP size" * `--min-keyint`: the "Minimum GOP size" > A GOP is "Group of Pictures" or the distance between two key frames. So lets re-encode with those options. Actually lets write a wrapper script to do this. I'll choose something besides bash because there will be a bit of math involved. ```python #!/usr/bin/env python import sys import json import subprocess import logging logging.basicConfig(level=logging.DEBUG) def probe_info(infname): cmd = f'ffprobe -v quiet -print_format json -show_format -show_streams {infname}'.split(' ') res = subprocess.run(cmd, check=False, capture_output=True) logging.info('running cmd %s', ' '.join(cmd)) ffprobe_dict = json.loads(res.stdout) v_stream = None for stream in ffprobe_dict.get('streams'): if stream.get('codec_type') == 'video': v_stream = stream break r_frame_rate = v_stream.get('r_frame_rate') num, denom = r_frame_rate.split('/') fps = float(num) / float(denom) logging.info('got fps %s', fps) return { 'fps': fps, } def run_ffmpeg_transcode(infname, outfname, probeinfo, segment_length=3): # must be an integer keyint = int(probeinfo.get('fps') * segment_length) cmd = [ 'ffmpeg', '-i', infname, '-vcodec', 'libx264', '-x264opts', f'keyint={keyint}:min-keyint={keyint}:no-scenecut', '-acodec', 'aac', outfname ] logging.info('running cmd %s', ' '.join(cmd)) subprocess.run(cmd, check=True) if __name__ == '__main__': args = sys.argv prog = args.pop(0) if len(args) != 2: sys.exit(1) infname, outfname = args probeinfo = probe_info(infname) run_ffmpeg_transcode(infname, outfname, probeinfo) ``` * Use `ffprobe` to dump the streams as json. * Take first video stream. * Get the `r_frame_rate` which is a fraction. Eval the fraction as `fps` * Calculate the keyframe interval using a static 3s segment length. And if we run it, lets take a look at the cmds it executes: ``` ❯ ./progressive.py ./test-videos/big_buck_bunny_720p_h264.mov ./test-videos/bbb_h264_aac.mp4 INFO:root:running cmd ffprobe -v quiet -print_format json -show_format -show_streams ./test-videos/big_buck_bunny_720p_h264.mov INFO:root:got fps 24.0 INFO:root:running cmd ffmpeg -i ./test-videos/big_buck_bunny_720p_h264.mov -vcodec libx264 -x264opts keyint=72:min-keyint=72:no-scenecut -acodec aac ./test-videos/bbb_h264_aac.mp4 ``` Now regenerate the frame dump and check if our I frames match the expected: 1, 73, 145, 217 ... ```shell ❯ ./dumpframes.sh test-videos/bbb_h264_aac.mp4 > bbb_frames.csv ❯ grep -n I ./bbb_vimeo_frames.csv | head 1:frame,I,H.26[45] User Data Unregistered SEI message 73:frame,I 145:frame,I 217:frame,I 286:frame,I 289:frame,I 361:frame,I 379:frame,I 433:frame,I 505:frame,I ``` Excellent! [pic_types]: https://en.wikipedia.org/wiki/Video_compression_picture_types [apple_hls_seg]: https://developer.apple.com/documentation/http-live-streaming/hls-authoring-specification-for-apple-devices#Media-Segmentation