[FFmpeg-devel] Audio decoding in api-example.c broken?

[Michael Niedermayer]

On Mon, May 24, 2010 at 10:42:41AM +0300, Martin Storsj? wrote:
> On Mon, 24 May 2010, Michael Niedermayer wrote:
> 
> > a AVParser could be used or you could implement some buffer that is refilled
> > after each frame is decoded
> 
> An attempt at solving it by refilling the buffer is attached.
> 
> // Martin
>  api-example.c |   12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> f62159abacf81c6c15a0a4f310284b9f6d2859e4  0001-Refill-the-input-audio-buffer-after-decoding-each-pa.patch
> From 25f9c3322ebe7381623ddb546d61c67540267835 Mon Sep 17 00:00:00 2001
> From: Martin Storsjo <martin at martin.st>
> Date: Mon, 24 May 2010 10:23:25 +0300
> Subject: [PATCH] Refill the input audio buffer after decoding each packet
> 
> This avoids trying to decode incomplete frames.
> ---
>  libavcodec/api-example.c |   12 ++++++------
>  1 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/libavcodec/api-example.c b/libavcodec/api-example.c
> index fb48b1f..576826d 100644
> --- a/libavcodec/api-example.c
> +++ b/libavcodec/api-example.c
> @@ -155,12 +155,8 @@ static void audio_decode_example(const char *outfilename, const char *filename)
>  
>      /* decode until eof */
>      avpkt.data = inbuf;
> -    for(;;) {
>          avpkt.size = fread(inbuf, 1, INBUF_SIZE, f);
> -        if (avpkt.size == 0)
> -            break;
>  
> -        avpkt.data = inbuf;
>          while (avpkt.size > 0) {
>              out_size = AVCODEC_MAX_AUDIO_FRAME_SIZE;
>              len = avcodec_decode_audio3(c, (short *)outbuf, &out_size, &avpkt);
> @@ -173,9 +169,13 @@ static void audio_decode_example(const char *outfilename, const char *filename)
>                  fwrite(outbuf, 1, out_size, outfile);
>              }
>              avpkt.size -= len;
> -            avpkt.data += len;
> +            memmove(avpkt.data, avpkt.data + len, avpkt.size);
> +            /* Refill the input buffer, to avoid trying to decode
> +             * incomplete frames. */
> +            len = fread(avpkt.data + avpkt.size, 1, INBUF_SIZE - avpkt.size, f);
> +            if (len > 0)
> +                avpkt.size += len;

as this is an example people will use for their applications
it should mention parsers and demuxers as alternative solutions
and the refill must be implemented so as to minimize memmove/cpy
moving is only needed once we get close to the end of the buffer ...


[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Avoid a single point of failure, be that a person or equipment.
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