[FFmpeg-devel] [PATCH]Fix AC3-in-avi for the remaining cases
Justin Ruggles
justin.ruggles
Sun Jan 2 04:41:15 CET 2011
On 01/01/2011 10:14 PM, Michael Niedermayer wrote:
> On Sat, Jan 01, 2011 at 03:52:07PM -0500, Justin Ruggles wrote:
>> On 01/01/2011 03:03 PM, Carl Eugen Hoyos wrote:
>>
>>> Hi!
>>>
>>> Current svn produces avi files that don't playback on any player when muxing
>>> AC3 with 32kHz/320kB, 32kHz/384kB and 44.1kHz/384kB.
>>> I believe Justin suggested to set blkalign to maximum frame size (first
>>> patch).
>>> An alternative is to just fix the failing cases (second patch).
>>>
>>> Opinions?
>>>
>>> Please comment, Carl Eugen
>>>
>>>
>>
>>> Index: libavformat/riff.c
>>> ===================================================================
>>> --- libavformat/riff.c (revision 26183)
>>> +++ libavformat/riff.c (working copy)
>>> @@ -370,12 +370,10 @@
>>> av_log(enc, AV_LOG_WARNING, "requested bits_per_coded_sample (%d) and actually stored (%d) differ\n", enc->bits_per_coded_sample, bps);
>>> }
>>>
>>> - if (enc->codec_id == CODEC_ID_MP2 || enc->codec_id == CODEC_ID_MP3 || enc->codec_id == CODEC_ID_AC3) {
>>> + if (enc->codec_id == CODEC_ID_MP2 || enc->codec_id == CODEC_ID_MP3) {
>>> blkalign = enc->frame_size; //this is wrong, but it seems many demuxers do not work if this is set correctly
>>> //blkalign = 144 * enc->bit_rate/enc->sample_rate;
>>> - //For high bitrate AC-3, set blkalign to maximum bytes per frame value
>>> - //to allow playback on WMP and MPlayer
>>> - if (enc->bit_rate > 384000)
>>> + } else if (enc->codec_id == CODEC_ID_AC3) {
>>> blkalign = 3840;
>>> } else if (enc->codec_id == CODEC_ID_ADPCM_G726) { //
>>> blkalign = 1;
>>
>>
>> I like this version better.
>>
>> Regarding the other patch, if it would be better for some reason to use
>> a more accurate value for AC-3 we could do:
>
> being exact when there is exactly just 1 packet size is nice, beyond that its
> a hack either way
Well, there is such thing as VBR AC-3 so using the maximum value for the
given sample rate is at least less of a hack. The exact value can be
calculated if it is CBR.
>> switch (enc->sample_rate) {
>> 8000: blkalign = 960;
>> 11025: blkalign = 697;
>> 12000: blkalign = 640;
>> 16000: blkalign = 1920;
>> 22050: blkalign = 1394;
>> 24000: blkalign = 1280;
>> 32000: blkalign = 3840;
>> 44100: blkalign = 2788;
>> 48000: blkalign = 2560;
>> }
>
> Is this how our encoder behaves or is this required by spec?
This is the maximum frame size (640 kbps) for AC-3 per spec and for our
encoder for each supported sample rate. Well, the last 3 are per spec.
Technically the others don't have a spec, but they're supported by our
encoder, our decoder, liba52, and RealPlayer.
-Justin
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