[FFmpeg-user] Identifying an MP4 file

[Carl Eugen Hoyos]

Sreenath BH <bhsreenath <at> gmail.com> writes:

> We have a HTTP Live Streaming (HLS) setup where we transcode 
> incoming video files to H264 video and AAC audio and build 
> playlist files from that. We want to avoid this step if the 
> input file is already a MP4 file.

This is difficult to understand:
HLS uses mpeg-ts, mp4 is a different container.

> I know that MP4 is just a container and does not imply H264 
> and AAC.

This is correct.

> I am planning to check the audio and video codec IDs in our 
> program after getting the stream information using 
> avformat_find_stream_info.

avformat_find_stream_info tells you about the codecs used in 
the stream, it does not tell you which container the stream 
has (this has to be determined before).

> So, if the video codec ID and Audio codec ID are respectively,
> 
> AV_CODEC_ID_H264 and AV_CODEC_ID_AAC
> 
> Is it sufficient to qualify it as a MP4 file?

No, because H264 and AAC can be found in (many) other containers.

> The reason I ask is that there are some flv files that use 
> the same codecs, but I am not sure if it would be safe it 
> to treat it on par with an "authentic" mp4 file.

An flv and an mp4 file are definitely two different things.
(While an f4v file is an mp4 file.)

Carl Eugen