Media conversion

Media conversion

Updated
Appears in: Media

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
Gotchas!

Technically, FFmpeg always requires an output file format. Calling FFmpeg this way will give you an error message explaining that; however, it lists information not available using Shaka Packager so feel free to ignore the error.

Demux (separate) the audio and video streams #

Shaka Packager requires demuxing when converting files. This is also required for using media frameworks.

Shaka Packager demuxing #

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 demuxing #

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 .mp4 or .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 .mov files and hence cannot be used to convert files from that format.

.mov to .mp4

ffmpeg -i myvideo.mov myvideo.mp4

.mov to .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

Visit Containers and codecs to view the audio and video codecs and the associated encoding and decoding library the codec uses.

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 and web-standards-based method of presenting video-on-demand. The second is HTTP Live Streaming (HLS), which is Apple's standard for 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 an M3U8 output 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 encryption next.

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