On Wed, Mar 07, 2018 at 03:30:37PM +0100, Philipp M. Scholl wrote:
> Here is the fourth version of the PCM patch with updated testcases.
>
> The blocksize of the PCM decoder is hard-coded. This creates
> unnecessary delay when reading low-rate (<100Hz) streams. This creates
> issues when multiplexing multiple streams, since other inputs are only
> opened/read after a low-rate input block was completely read.
>
> This patch decreases the blocksize for low-rate inputs, so
> approximately a block is read every 40ms. This decreases the startup
> delay when multiplexing inputs with different rates.
>
> Signed-off-by: Philipp M. Scholl <psch...@bawue.de>
> ---
> libavformat/pcm.c | 16 ++++++++++++----
> tests/ref/seek/lavf-alaw | 42 +++++++++++++++++++++---------------------
> tests/ref/seek/lavf-mulaw | 42 +++++++++++++++++++++---------------------
> 3 files changed, 54 insertions(+), 46 deletions(-)
>
> diff --git a/libavformat/pcm.c b/libavformat/pcm.c
> index 806f91b6b..1ea15a9e8 100644
> --- a/libavformat/pcm.c
> +++ b/libavformat/pcm.c
> @@ -28,13 +28,21 @@
>
> int ff_pcm_read_packet(AVFormatContext *s, AVPacket *pkt)
> {
> - int ret, size;
> + int ret, size = INT_MAX;
> + AVCodecParameters *par = s->streams[0]->codecpar;
>
> - size= RAW_SAMPLES*s->streams[0]->codecpar->block_align;
> - if (size <= 0)
> + if (par->block_align <= 0)
> return AVERROR(EINVAL);
>
> - ret= av_get_packet(s->pb, pkt, size);
> + /*
> + * Compute read size to complete a read every 40ms. Clamp to
> RAW_SAMPLES if
> + * larger. Use power of two as readsize for I/O efficiency.
> + */> + size = FFMAX(par->sample_rate/25, 1); division is a bit slowish, and this is done per (small) packet. Maybe a >>4 or >>5 could be used ? (this is a minor issue) > + size = FFMIN(size, RAW_SAMPLES) * par->block_align; > + size = 1 << ff_log2(size); > + > + ret = av_get_packet(s->pb, pkt, size); what if block_align is not a power of 2? for example with 6 channels there could be a reasonable block size that is not a multiple of 2. or am i missing something ? [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Complexity theory is the science of finding the exact solution to an approximation. Benchmarking OTOH is finding an approximation of the exact
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