[FFmpeg-devel] [PATCH 1/2] avformat/movenc: fix sample size being zero in pcmC

[FFmpeg-devel] [PATCH 1/2] avformat/movenc: fix sample size being zero in pcmC

[Zhao Zhili]

From: Zhao Zhili <zhilizhao@tencent.com>

bits_per_raw_sample might not set when remux raw PCM.

Fix #10433.
---
 libavformat/movenc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index f1cc80b1b3..7ef6cef46a 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -1225,6 +1225,7 @@ static int mov_write_pcmc_tag(AVFormatContext *s, AVIOContext *pb, MOVTrack *tra
 {
     int64_t pos = avio_tell(pb);
     int format_flags;
+    int sample_size;
 
     avio_wb32(pb, 0); /* size */
     ffio_wfourcc(pb, "pcmC");
@@ -1237,7 +1238,11 @@ static int mov_write_pcmc_tag(AVFormatContext *s, AVIOContext *pb, MOVTrack *tra
                     track->par->codec_id == AV_CODEC_ID_PCM_S24LE ||
                     track->par->codec_id == AV_CODEC_ID_PCM_S32LE);
     avio_w8(pb, format_flags);
-    avio_w8(pb, track->par->bits_per_raw_sample);
+    sample_size = track->par->bits_per_raw_sample;
+    if (!sample_size)
+        sample_size = av_get_exact_bits_per_sample(track->par->codec_id);
+    av_assert0(sample_size);
+    avio_w8(pb, sample_size);
 
     return update_size(pb, pos);
 }
-- 
2.34.1

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Re: [FFmpeg-devel] [PATCH 1/2] avformat/movenc: fix sample size being zero in pcmC

[Raphaël Zumer]

On 7/25/23 23:45, Zhao Zhili wrote:
> From: Zhao Zhili <zhilizhao@tencent.com>
>
> -    avio_w8(pb, track->par->bits_per_raw_sample);
> +    sample_size = track->par->bits_per_raw_sample;
> +    if (!sample_size)
> +        sample_size = av_get_exact_bits_per_sample(track->par->codec_id);
> +    av_assert0(sample_size);
> +    avio_w8(pb, sample_size);

Why not just replace bits_per_raw_sample completely with av_get_exact_bits_per_sample()?

Are there edge cases, like incorrect codec ID, or sample sizes smaller than specified by the codec ID (and if there is ever a mismatch, which is expected in pcmC?)

If not, there should be no need to prioritize bits_per_raw_sample in the first place and add a fallback - going straight to av_get_exact_bits_per_sample() should suffice and keep the code simpler.

As noted in another thread, bits_per_raw_sample seems to always be 0 when muxing PCM to MP4 with FFmpeg, whereas bits_per_coded_sample has the correct value from the samples that I tested.

Raphaël Zumer

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Re: [FFmpeg-devel] [PATCH 1/2] avformat/movenc: fix sample size being zero in pcmC

[Zhao Zhili]

> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Raphaël Zumer
> Sent: 2023年7月26日 21:38
> To: ffmpeg-devel@ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH 1/2] avformat/movenc: fix sample size being zero in pcmC
> 
> On 7/25/23 23:45, Zhao Zhili wrote:
> > From: Zhao Zhili <zhilizhao@tencent.com>
> >
> > -    avio_w8(pb, track->par->bits_per_raw_sample);
> > +    sample_size = track->par->bits_per_raw_sample;
> > +    if (!sample_size)
> > +        sample_size = av_get_exact_bits_per_sample(track->par->codec_id);
> > +    av_assert0(sample_size);
> > +    avio_w8(pb, sample_size);
> 
> Why not just replace bits_per_raw_sample completely with av_get_exact_bits_per_sample()?
> 
> Are there edge cases, like incorrect codec ID, or sample sizes smaller than specified by the codec ID (and if there is ever a mismatch,
> which is expected in pcmC?)
> 
> If not, there should be no need to prioritize bits_per_raw_sample in the first place and add a fallback - going straight to
> av_get_exact_bits_per_sample() should suffice and keep the code simpler.

Check bits_per_raw_sample first for a little bit of performance.
Don't use bits_per_coded_sample because it make less sense in this case and to keep the code simpler.

> 
> As noted in another thread, bits_per_raw_sample seems to always be 0 when muxing PCM to MP4 with FFmpeg, whereas
> bits_per_coded_sample has the correct value from the samples that I tested.

That's only one usecase. bits_per_coded_sample has been set while bit_per_raw_sample wasn't only
because the implementation of wav demux and there's no encoding process. (You can try -c:a pcm_s16le)

There are more usecases to support, e.g., only use mp4 muxer without any demuxer or encoder.
User can create and set a AVCodecParameters manually, and let bits_per_coded_sample be zero.

> 
> Raphaël Zumer
> 
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Re: [FFmpeg-devel] [PATCH 1/2] avformat/movenc: fix sample size being zero in pcmC

[Raphaël Zumer]

On 7/26/23 11:22, Zhao Zhili wrote:
>> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Raphaël Zumer
>> Sent: 2023年7月26日 21:38
>> To: ffmpeg-devel@ffmpeg.org
>> Subject: Re: [FFmpeg-devel] [PATCH 1/2] avformat/movenc: fix sample size being zero in pcmC
>>
>> On 7/25/23 23:45, Zhao Zhili wrote:
>>> From: Zhao Zhili <zhilizhao@tencent.com>
>>>
>>> -    avio_w8(pb, track->par->bits_per_raw_sample);
>>> +    sample_size = track->par->bits_per_raw_sample;
>>> +    if (!sample_size)
>>> +        sample_size = av_get_exact_bits_per_sample(track->par->codec_id);
>>> +    av_assert0(sample_size);
>>> +    avio_w8(pb, sample_size);
>> Why not just replace bits_per_raw_sample completely with av_get_exact_bits_per_sample()?
>>
>> Are there edge cases, like incorrect codec ID, or sample sizes smaller than specified by the codec ID (and if there is ever a mismatch,
>> which is expected in pcmC?)
>>
>> If not, there should be no need to prioritize bits_per_raw_sample in the first place and add a fallback - going straight to
>> av_get_exact_bits_per_sample() should suffice and keep the code simpler.
> Check bits_per_raw_sample first for a little bit of performance.
> Don't use bits_per_coded_sample because it make less sense in this case and to keep the code simpler.
I doubt it is worth the trouble, but my opinion is not important if no one else cares.
>> As noted in another thread, bits_per_raw_sample seems to always be 0 when muxing PCM to MP4 with FFmpeg, whereas
>> bits_per_coded_sample has the correct value from the samples that I tested.
> That's only one usecase. bits_per_coded_sample has been set while bit_per_raw_sample wasn't only
> because the implementation of wav demux and there's no encoding process. (You can try -c:a pcm_s16le)
>
> There are more usecases to support, e.g., only use mp4 muxer without any demuxer or encoder.
> User can create and set a AVCodecParameters manually, and let bits_per_coded_sample be zero.

That is fair, I just wanted to point out the mismatch as a potential (separate) issue.

RZ

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