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When playing a MP4 file VLC tells me the video and audio codecs are mp4v and mp4a. The quality is good at low bitrates. However, the MP4 Streaming Faq tells me that mp4v means raw MPEG4 streams. What does this mean? It clearly isn't unencoded video.

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2 Answers 2

VLC is telling you the truth - it looks to me (without actually seeing the file) that your MP4 file is a MPEG-4 container with MPEG-4 codecs being used for the audio and video.

MPEG-4 is both a container and a codec:

MPEG-4 is a form of MPEG encoding. It is a flexible audio and video compression format. The format describes audio and video compression, with a container format for streaming across networks and saving to disk. It also contains optional extra features, including DRM and subtitles. These extra features are only included in software if needed. MPEG-4 can provide better quality than MPEG-2 at low bitrates.

MPEG-4 audio is an advanced, complicated audio format. It includes AAC for high bitrates, multilingual tracks, text-to-speech modes for very low bitrates, the ability to synthesize instrumental sounds (similar to MIDI), and more.

Video:

mp4v

This is a video codec.
This codec can be used inside the MPEG-4 containers.
This codec is from the ffmpeg module.

Audio:

mp4a

This is an audio codec.
This codec can be used inside the MPEG-4 containers.
This codec is from the ffmpeg module.

If we were talking about the MP4 container, you could see these types of codecs in them:

Accepted video codecs
mp4v, including all the codecs described above
mpgv MJPG
mjpb
SVQ1
SVQ3
H263
h264

Accepted audio codecs
mp4a (is aac)
mpga
samr
sawb

Accepted subtitle codec
subt

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MP4V and MP4A stand for Mpeg 4 Video and Audio.

From Wikipedia:

MPEG-4 is a patented collection of methods defining compression of audio and visual (AV) digital data

From VideoLan:

MPEG-4 specifies a range of codecs

The fourccs of MPEG-4 codecs are:

o DivX Codecs
      o DIV1, div1, DIVX, divx, DX50, dx50, XVID, XviD, xvid 
o FFMPEG MPEG-4
      o FMP4, fmp4 
o 3IV2, 3iv2
o BLZ0
o DXGM
o HDX4, hdx4
o M4S2, m4s2
o MP4S, mp4s
o MP4V, mp4v
o RMP4
o SEDG
o SMP4
o UMP4
o WV1F
o XVIX

For better clarification of actual codecs used try:

MediaInfo

or

GraphEdit

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So mp4v indicates that something is an MPEG4 video stream without disclosing the actual codec used? Or is mp4v a codec itself? –  StackedCrooked Mar 10 '10 at 11:09
    
it would appear that your first statement is correct. Open the file in MediaInfo to confirm. –  Shevek Mar 10 '10 at 11:22
    
This isn't entirely correct - MP4 is both a container AND a codec (see my answer for the gory details). VLC is telling you about the codecs being used. –  Jared Harley Mar 10 '10 at 12:11
    
Well, I learnt something today then! ;) –  Shevek Mar 10 '10 at 13:02

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