[FFmpeg-devel] [PATCH] WAV file length (writing to stdout)
Fri Oct 19 15:15:17 CEST 2007
Justin Ruggles writes:
> Axel Holzinger wrote:
> > Rich Felker writes:
> >> On Tue, Oct 16, 2007 at 05:02:39PM +0200, Cyril B. wrote:
> >>> Hi,
> >>> As reported recently on this mailing list , ffmpeg sets
> >> 0 as file length
> >>> in the WAV header if output is streamed (for instance, when
> >> outputting to
> >>> stdout). Nero AAC encoder does not accept such streams
> >> ('could not parse
> >>> WAV file' error).
> >>> The WAV file specs  say the file length (ChunkSize) must
> >> be 36 + data
> >>> length. The included patch writes 36 instead of 0, which
> >> satisfies Nero
> >>> encoder.
> >> IMO both are wrong. The most compatible way to make a wav
> header for
> >> unknown length is to put 0xffffffff in the header.
> > 0 as the RIFF length and 0 as the data chunk length is a
> common agreement in serious recording applications while
> still recording the file. So a playback application can
> determine that the given file is still being recorded. As
> soon as the recording application finishes the ongoing
> recording, it writes the correct values for RIFF lenth and
> data chunk length to the file.
> > I think Nero AAC encoder is an application that is not
> considering that a given file might still be recorded at the
> moment it is passed to Nero AAC encoder.
> > Setting theboth length to 0xffffffff (-1) makes the file
> invalid as 0xffffffff (-1) is an invalid value for the lenth
> fields. So I consider this to not be a good way.
> The length is treated as unsigned, so 4294967295 is a valid
> length. But
> there are many programs which use this convention because it has the
> effect of saying "keep reading data until the end-of-file".
> There are
> only a couple downsides. One is that a program may report
> the playing
> time as something like 6 hours instead of the actual playing time.
> Another is that no other chunks can follow the DATA chunk.
0xFFFFFFFF being invalif as a RIFF length has nothing to do
with signed/unsigend (clearly it is unsigned), but with the
fact that The RIFF length is a even number by the spec.
Also the length of the data chunk is even (that's what the RIFF/WAVE
spec defines). If you have 8 bit mono you have to add a padding byte.
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