In this article we are going to learn some common commands for converting and manipulating specific characteristics of media files. Although we've tried to show equivalent operations for all procedures, not all operations are possible in both applications.
In many cases, the commands we're showing may be combined in a single command line operation, and would be when actually used. For example, there's nothing preventing you from setting an output file's bitrate in the same operation as a file conversion. For this article, we often show these operations as separate commands for the sake of clarity.
Conversion is done with these applications:
Display characteristics
Both Shaka Packager and FFmpeg can be used to inspect the content of a media file and then display the characteristics of a stream. However, both provide different output for the same media.
Characteristics using Shaka Packager
packager input=glocken.mp4 --dump_stream_info
The output looks like:
File "glocken.mp4":
Found 2 stream(s).
Stream [0] type: Video
codec_string: avc1.640028
time_scale: 30000
duration: 300300 (10.0 seconds)
is_encrypted: false
codec: H264
width: 1920
height: 1080
pixel_aspect_ratio: 1:1
trick_play_factor: 0
nalu_length_size: 4
Stream [1] type: Audio
codec_string: mp4a.40.2
time_scale: 48000
duration: 481280 (10.0 seconds)
is_encrypted: false
codec: AAC
sample_bits: 16
num_channels: 2
sampling_frequency: 48000
language: eng
seek_preroll_ns: 20833
Characteristics using FFmpeg
ffmpeg -i glocken.mp4
The output looks like:
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'glocken.mp4':
Metadata:
major_brand: isom
minor_version: 512
compatible_brands: isomiso2avc1mp41
encoder: Lavf57.83.100
Duration: 00:00:10.03, start: 0.000000, bitrate: 8063 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc), 1920x1080, 7939 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default)
Metadata:
handler_name: VideoHandler
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 127 kb/s (default)
Metadata:
handler_name: SoundHandler
At least one output file must be specified
Demux (separate) the audio and video streams
Shaka Packager requires demu xing when converting files. This is also required for using media frameworks.
Shaka Packager demu xing
MP4
packager input=myvideo.mp4,stream=video,output=myvideo_video.mp4
packager input=myvideo.mp4,stream=audio,output=myvideo_audio.m4a
Or:
packager \
input=myvideo.mp4,stream=video,output=myvideo_video.mp4 \
input=myvideo.mp4,stream=audio,output=myvideo_audio.m4a
WebM
packager \
input=myvideo.webm,stream=video,output=myvideo_video.webm \
input=myvideo.webm,stream=audio,output=myvideo_audio.webm
FFmpeg demu xing
MP4
ffmpeg -i myvideo.mp4 -vcodec copy -an myvideo_video.mp4
ffmpeg -i myvideo.mp4 -acodec copy -vn myvideo_audio.m4a
WebM
ffmpeg -i myvideo.webm -vcodec copy -an myvideo_video.webm
ffmpeg -i myvideo.webm -acodec copy -vn myvideo_audio.webm
Remux (combine) the audio and video streams
In some situation you will need to combine the audio and video back into a single container. Especially when not using a media framework. This is something FFmpeg can handle quite well and is something Shaka Packager does not currently support.
ffmpeg -i myvideo_video.webm -i myvideo_audio.webm -c copy myvideo.webm
Change characteristics
Bitrate
For FFmpeg, we can do this while converting to.mp4or.webm.
ffmpeg -i myvideo.mov -b:v 350K myvideo.mp4
ffmpeg -i myvideo.mov -vf setsar=1:1 -b:v 350K myvideo.webm
Dimensions (resolution)
ffmpeg -i myvideo.webm -s 1920x1080 myvideo_1920x1080.webm
File type
Shaka Packager cannot process.movfiles and hence cannot be used to convert
files from that format.
.movto.mp4
ffmpeg -i myvideo.mov myvideo.mp4
.movto.webm
ffmpeg -i myvideo.mov myvideo.webm
Synchronize audio and video
To ensure that audio and video synchronize during playback, insert keyframes.
ffmpeg -i myvideo.mp4 -keyint_min 150 -g 150 -f webm -vf setsar=1:1 out.webm
MP4/H.264
ffmpeg -i myvideo.mp4 -c:v libx264 -c:a copy myvideo.mp4
Audio for an MP4
ffmpeg -i myvideo.mp4 -c:v copy -c:a aac myvideo.mp4
WebM/VP9
ffmpeg -i myvideo.webm -v:c libvpx-vp9 -v:a copy myvideo.webm
Audio for a WebM
ffmpeg -i myvideo.webm -v:c copy -v:a libvorbis myvideo.webm
ffmpeg -i myvideo.webm -v:c copy -v:a libopus myvideo.webm
Video-on-demand and live-streaming
There are two types of streaming protocols we are going to demonstrate in this article. The first is Dynamic Adaptive Streaming over HTTP (DASH), which is an adaptive bitrate streaming technique andweb-standards-basedmethod of presenting video-on-demand. The second is HTTP Live Streaming (HLS), which is Apple's standardfor live-streaming and video-on-demand for the web.
DASH/MPD
This example generates the Media Presentation Description (MPD) output file from the audio and video streams.
packager \
input=myvideo.mp4,stream=audio,output=myvideo_audio.mp4 \
input=myvideo.mp4,stream=video,output=myvideo_video.mp4 \
--mpd_output myvideo_vod.mpd
HLS
These examples generate anM3U8output file from the audio and video streams,
which is a UTF-8 encoded multimedia playlist.
ffmpeg -i myvideo.mp4 -c:a copy -b:v 8M -c:v copy -f hls \
-hls_time 10 -hls_list_size 0 myvideo.m3u8
OR:
packager \
'input=myvideo.mp4,stream=video,segment_template=output$Number$.ts,playlist_name=video_playlist.m3u8' \
'input=myvideo.mp4,stream=audio,segment_template=output_audio$Number$.ts,playlist_name=audio_playlist.m3u8,hls_group_id=audio,hls_name=ENGLISH' \
--hls_master_playlist_output= "master_playlist.m3u8"
Now that we hopefully have a good grasp on how to convert files, we can build on what we've learned in this article and go learn about Media encryptionnext.