![Derek Herman](https://web.dev/images/authors/derekherman.jpg) Derek Herman [X](https://twitter.com/derekherman) [GitHub](https://github.com/derekherman) ![Joe Medley](https://web.dev/images/authors/joemedley.jpg) Joe Medley [GitHub](https://github.com/jpmedley)
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: - [Shaka Packager](https://github.com/google/shaka-packager) ([on Stack Overflow](https://stackoverflow.com/questions/tagged/shaka)) - [FFmpeg](https://ffmpeg.org/download.html), ([on Stack Overflow](https://stackoverflow.com/questions/tagged/ffmpeg)) ## 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 ```bash packager input=glocken.mp4 --dump_stream_info ``` The output looks like: ```bash 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 ```bash ffmpeg -i glocken.mp4 ``` The output looks like: ```bash 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 ``` > [!TIP] > 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** ```bash packager input=myvideo.mp4,stream=video,output=myvideo_video.mp4 packager input=myvideo.mp4,stream=audio,output=myvideo_audio.m4a ``` Or: ```bash packager \ input=myvideo.mp4,stream=video,output=myvideo_video.mp4 \ input=myvideo.mp4,stream=audio,output=myvideo_audio.m4a ``` **WebM** ```bash packager \ input=myvideo.webm,stream=video,output=myvideo_video.webm \ input=myvideo.webm,stream=audio,output=myvideo_audio.webm ``` ### FFmpeg demuxing **MP4** ```bash ffmpeg -i myvideo.mp4 -vcodec copy -an myvideo_video.mp4 ffmpeg -i myvideo.mp4 -acodec copy -vn myvideo_audio.m4a ``` **WebM** ```bash 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. ```bash 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`. ```bash ffmpeg -i myvideo.mov -b:v 350K myvideo.mp4 ffmpeg -i myvideo.mov -vf setsar=1:1 -b:v 350K myvideo.webm ``` ### Dimensions (resolution) ```bash 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`** ```bash ffmpeg -i myvideo.mov myvideo.mp4 ``` **`.mov` to `.webm`** ```bash ffmpeg -i myvideo.mov myvideo.webm ``` ### Synchronize audio and video To ensure that audio and video synchronize during playback, insert keyframes. ```bash ffmpeg -i myvideo.mp4 -keyint_min 150 -g 150 -f webm -vf setsar=1:1 out.webm ``` > [!NOTE] > **Note:** Visit *Containers and codecs* to view the audio and video [**codecs**](https://web.dev/articles/containers-and-codecs.md.txt#codecs) and the associated encoding and decoding library the codec uses. ***MP4/H.264*** ```bash ffmpeg -i myvideo.mp4 -c:v libx264 -c:a copy myvideo.mp4 ``` ***Audio for an MP4*** ```bash ffmpeg -i myvideo.mp4 -c:v copy -c:a aac myvideo.mp4 ``` ***WebM/VP9*** ```bash ffmpeg -i myvideo.webm -v:c libvpx-vp9 -v:a copy myvideo.webm ``` ***Audio for a WebM*** ```bash 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](https://developer.mozilla.org/docs/Web/HTML/DASH_Adaptive_Streaming_for_HTML_5_Video) method of presenting video-on-demand. The second is HTTP Live Streaming (HLS), which is [Apple's standard](https://developer.apple.com/streaming/) 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. ```bash 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. ```bash 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: ```bash 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](https://web.dev/articles/media-encryption.md.txt) next.