Extract Audio from Video Files to WAV using FFmpeg

Posted by admin on December 15, 2009 under Tech Tips | Be the First to Comment

Previously, I described how to Extract Audio from Video Files to WAV using Mplayer. Another method using FFmpeg instead of Mplayer was also pointed out in the post titled Add Stereo Audio Tracks to MKV Files, and I figured it would be useful to outline the quick one-step process in a post all by itself.

Here’s an example of extracting the audio from a video file called video.mkv and saving it to a file called audio.wav. This very well could have been an AVI, MPEG, or any other video format that FFmpeg can decode.

ffmpeg -i video.mkv -acodec pcm_s16le -ac 2 audio.wav

It should also be mentioned that your source video file may have multiple audio channels or streams. For example, you may have both English AC3 and DTS channels, but you may also have other audio streams for other languages, directors comments, etc. If you want more control over which stream you are using, first identify them all with ffmpeg.

ffmpeg -i video.mkv
[snipped for brevity]
Input #0, matroska, from 'video.mkv':
Duration: 01:30:38.78, start: 0.000000, bitrate: N/A
Stream #0.0(eng): Video: h264, yuv420p, 1280x720, PAR 1:1 DAR 16:9, 23.98 tbr, 1k tbn, 47.95 tbc
Stream #0.1(eng): Audio: ac3, 48000 Hz, 5.1, s16
Stream #0.2(eng): Subtitle: 0x0000
Stream #0.3(heb): Audio: mp3, 48000 Hz, stereo, s16
Stream #0.4(heb): Subtitle: 0x0000
Stream #0.5: Attachment: 0x0000
Stream #0.6: Attachment: 0x0000
At least one output file must be specified

From the example above, you see that Stream #0.0 is labeled as being an English video stream with h264 encoding. Stream #0.1 and #0.3 are both audio streams, but #0.1 is English AC3 5.1 and #0.3 is Hebrew MP3 stereo. Simply reference the stream id with the -map option in the following format.

ffmpeg -i video.mkv -map 0:1 -acodec pcm_s16le -ac 2 audio.wav
[snipped for brevity]
Output #0, wav, to 'audio.wav':
Stream #0.0(eng): Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
Stream mapping:
Stream #0.1 -> #0.0
[snipped for brevity]

Now that you have a PCM WAV file, you can manipulated it however you like, e.g. encode to MP3, OGG, FLAC, etc.

lame -V0 -q0 --vbr-new audio.wav audio.mp3
oggenc -q6 audio.wav
flac audio.wav

Extract Audio from Video Files to WAV using Mplayer

Posted by admin on October 11, 2009 under Tech Tips | Be the First to Comment

You can extract the audio from a video file using mplayer and save the result to a WAV file, which you can then manipulate to your hearts content. For example, you may want to compress the audio to a stereo MP3 or OGG.

The following command instruct that the audio output (-ao) should be redirected out to a PCM WAV file as fast as possible, while suppressing all video output.

mplayer -ao pcm:fast:file=audio.wav -vo null -vc null video.avi

Convert the resulting WAV to MP3. The following is a great way to convert your WAV files to a high quality Variable Bitrate MP3. See the man page for a decent tutorial on the available options.

lame -V0 -q0 --vbr-new audio.wav audio.mp3

Add Stereo Audio Tracks to MKV Files

Posted by admin on September 26, 2009 under Tech Tips | Be the First to Comment

If you have Matroska Video (MKV) files encoded with AC3 Dolby Digital 5.1 or DTS audio tracks, you may want to simply extract the audio, convert it to a 2-channel stereo format like WAV, MP3 OGG, etc, and then add it back into the MKV as a separate audio track. This is useful when your media player (e.g. Western Digital Media Player WDAVN00) will not downscale the audio from a digital format like AC3 or DTS to stereo when you don’t have a receiver or TV with a built in Dolby Digital decoder.  Now you’ll have the choice of either audio format depending on your technical requirements.

The great thing about the Matroska multimedia container is that you can easily manipulate these files without having to re-encode, saving lots of time. I’ll be using mkvextract to extract the AC3 audio, ffmpeg to convert ac3 to mp3, and finally mkvmerge to add and remux the new audio track to the MKV container. All of these are available to a number of platforms, but in my examples, I’m using Linux.  Check out the MKVToolnix and FFMpeg websites for more info on the software.

If using Ubuntu Linux, install the relevant mkvtoolnix,  mkvtoolnix-gui and ffmpeg packages.

sudo apt-get install mkvtoolnix mkvtoolnix-gui ffmpeg libavcodec-unstripped-52

To view the existing tracks of the MKV, use the mkvmerge -i option. In the following example, you see my “Cool.Video.mkv” file has an MPEG4 video in track 1, an AC3 Dolby Digital audio file in track 2, and subtitles in track 3.

mkvmerge -i Cool.Movie.mkv 
File 'Cool.Movie.mkv': container: Matroska
Track ID 1: video (V_MPEG4/ISO/AVC)
Track ID 2: audio (A_AC3)
Track ID 3: subtitles (S_TEXT/UTF8)

Using mkvextract, extract the AC3 Dolby Digital audio from track 2, saving it to a file called audio.ac3.

mkvextract tracks Cool.Movie.mkv 2:audio.ac3
Extracting track 2 with the CodecID 'A_AC3' to the file 'audio.ac3'. Container format: Dolby Digital (AC3)
Progress: 100%

ls -lh audio.ac3
-rw-r--r-- 1 gmendoza gmendoza 432M 2009-09-26 11:58 audio.ac3

Convert the 6-channel ac3 file to a 2-channel stereo MP3 using ffmpeg. If you prefer a higher audio bitrate, adjust the -ab value as desired. e.g. 256, 384, etc, and adjust the audio rate to your liking as well.

ffmpeg -i audio.ac3 -acodec libmp3lame -ab 160k -ac 2 audio.mp3
[output omitted for brevity]

ls -lh audio.*
-rw-r--r-- 1 gmendoza gmendoza 432M 2009-09-26 11:58 audio.ac3
-rw-r--r-- 1 gmendoza gmendoza 87M 2009-09-26 12:08 audio.mp3

To simplify things, you could actually skip the digital format extraction process by running ffmpeg against the MKV file directly.

ffmpeg -i Cool.Movie.mkv -acodec libmp3lame -ab 160k -ac 2 audio.mp3

If you prefer encoding with more advanced options, you could extract the audio as a 2-channel WAV file instead, and then process it with LAME, Oggenc, or some other encoder of your choosing. The following shows the extraction to WAV, and then conversion to various formats for fun, e.g. MP3, OGG, and FLAC.

ffmpeg -i Cool.Movie.mkv -acodec pcm_s16le -ac 2 audio.wav
lame -V0 -q0 --vbr-new audio.wav audio.mp3
oggenc -q6 audio.wav
flac audio.wav

Use mkvmerge to combine the original MKV with the MP3 audio track to create a new file called Cool.Movie.New.mkv. Make sure you have enough disk space for both the original and new MKV file.

mkvmerge -o Cool.Movie.New.mkv Cool.Movie.mkv audio.mp3
mkvmerge v2.4.1 ('Use Me') built on Dec 13 2008 21:03:46
'Cool.Movie.mkv': Using the Matroska demultiplexer.
'audio.mp3': Using the MP2/MP3 demultiplexer.
Warning: 'audio.mp3': Skipping 32 bytes at the beginning (no valid MP3 header found).
'Cool.Movie.mkv' track 1: Using the MPEG-4 part 10 (AVC) video output module.
'Cool.Movie.mkv' track 2: Using the AC3 output module.
'Cool.Movie.mkv' track 3: Using the text subtitle output module.
'audio.mp3' track 0: Using the MPEG audio output module.
The file 'Cool.Movie.New.mkv' has been opened for writing.
Progress: 100%
The cue entries (the index) are being written...
Muxing took 270 seconds.

Verify that the audio track has been added. You can see Track ID 4 has been successfully added.

mkvmerge -i New.Cool.Movie.mkv 
File 'New.Cool.Movie.mkv': container: Matroska
Track ID 1: video (V_MPEG4/ISO/AVC)
Track ID 2: audio (A_AC3)
Track ID 3: subtitles (S_TEXT/UTF8)
Track ID 4: audio (A_MPEG/L3)

That’s really all there is to it. There are quite a few options available when editing MKV container files. For example, I wanted nice descriptions for my tracks since various media players will read and display them for you during menu navigation. I recommend using the mkvmerge gui application as shown in this screenshot.

mkvmerge-gui

It’s really just a front-end application to mkvmerge, and the following text shows the commands that were used to specify the language for each tag, re-order the audio tracks, disable subtitles by default, and give useful descriptions to each Track ID.

mkvmerge -o "Cool.Movie.New.mkv" \
--language 1:eng \
--track-name "1:Cool Movie (MPEG4)" \
--default-track 1:yes \
--display-dimensions 1:40x17 \
--language 2:eng \
--track-name "2:Dolby Digital 5.1 (AC3)" \
--default-track 2:yes \
--language 3:eng \
--track-name "3:English Subtitles" \
--default-track 3:no \
-a 2 -d 1 -s 3 Cool.Movie.mkv \
--language 0:eng \
--track-name "0:2-Channel Stereo (MP3)" \
--default-track 0:no \
-a 0 -D -S audio.mp3 \
--track-order 0:1,0:2,1:0,0:3

mkvmerge -i Cool.Movie.New.mkv
File 'Cool.Movie.New.mkv': container: Matroska
Track ID 1: video (V_MPEG4/ISO/AVC)
Track ID 2: audio (A_AC3)
Track ID 3: audio (A_MPEG/L3)
Track ID 4: subtitles (S_TEXT/UTF8)