[FFmpeg-devel] [PATCH+RFC] AVFrame for audio

[Michael Niedermayer]

On Wed, Oct 06, 2010 at 11:05:26AM -0400, Justin Ruggles wrote:
> Michael Niedermayer wrote:
> 
> > On Tue, Oct 05, 2010 at 04:55:12PM -0400, Justin Ruggles wrote:
> >> Michael Niedermayer wrote:
> >>
> >>> On Wed, Sep 29, 2010 at 09:20:04PM -0400, Justin Ruggles wrote:
> >>>> Hi,
> >>>>
> >>>> Peter Ross wrote:
> >>>>
> >>>>> On Thu, Sep 02, 2010 at 07:11:37PM -0400, Justin Ruggles wrote:
> >>>>>> Hi,
[...]
> >
> >>> [...]
> >>>> @@ -644,29 +677,49 @@
> >>>>  }
> >>>>  #endif
> >>>>  
> >>>> +#if LIBAVCODEC_VERSION_MAJOR < 53
> >>>>  int attribute_align_arg avcodec_decode_audio3(AVCodecContext *avctx, int16_t *samples,
> >>>>                           int *frame_size_ptr,
> >>>>                           AVPacket *avpkt)
> >>>>  {
> >>>> +    AVFrame frame;
> >>>> +    int ret, got_frame = 0;
> >>>> +
> >>>> +    avcodec_get_frame_defaults(&frame);
> >>>> +
> >>>> +    ret = avcodec_decode_audio4(avctx, &frame, &got_frame, avpkt);
> >>>> +
> >>>> +    if (ret >= 0 && got_frame) {
> >>>> +        *frame_size_ptr = frame.nb_samples * avctx->channels *
> >>>> +                          (av_get_bits_per_sample_format(avctx->sample_fmt) / 8);
> >>>> +
> >>>> +        /* ensure data will fit in the output buffer */
> >>>> +        if (*frame_size_ptr > AVCODEC_MAX_AUDIO_FRAME_SIZE) {
> >>>> +            av_log(avctx, AV_LOG_WARNING, "avcodec_decode_audio3 samples "
> >>>> +                   "truncated to AVCODEC_MAX_AUDIO_FRAME_SIZE\n");
> >>>> +            *frame_size_ptr = AVCODEC_MAX_AUDIO_FRAME_SIZE;
> >>>> +        }
> >>>> +
> >>>> +        memcpy(samples, frame.data[0], *frame_size_ptr);
> >>>  the default get_buffer() should return the appropriate
> >>> buffer for this case.
> >> I'm sorry, I don't understand your comment.
> > 
> > i mean (non functional psseudocode below to explain the idea)
> > avcodec_decode_audio3(){
> >     avctx->foobar= samples;
> >     ret = avcodec_decode_audio4(avctx, &frame, &got_frame, avpkt);
> >     ...
> >     assert(samples == frame.data[0]);
> > 
> > -----
> > default_get_buffer(){
> >     if(avctx->foobar)
> >         return avctx->foobar;
> > 
> > 
> > (and yes this cannot work for all theoretical decoders)
> 
> 
> I think I get it.  So avctx->foobar would be an optional user-supplied
> buffer (avctx->user_buffer?) that default_get_buffer() would return if
> it is non-NULL, right?

yes


> 
> The problem I see is this:
> avcodec_decode_audio3() would use avcodec_decode_audio4().
> avcodec_decode_audio4() allocates as large a buffer as is needed through
> get_buffer(), but the avcodec_decode_audio3() API only requires the
> user-supplied buffer to be AVCODEC_MAX_AUDIO_FRAME_SIZE.  Couldn't this
> lead to the decoder writing past the end of a user-supplied buffer if it
> isn't large enough?  I guess we could also add a field
> avctx->user_buffer_size?

yes, of course
it was just a rough idea ...

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When the tyrant has disposed of foreign enemies by conquest or treaty, and
there is nothing more to fear from them, then he is always stirring up
some war or other, in order that the people may require a leader. -- Plato
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