On Thu, Sep 20, 2012 at 12:05:11PM +0100, Måns Rullgård wrote:
> Benjamin Larsson <benja...@southpole.se> writes:
>
> > libavcodec/a64multienc.c: In function ‘a64multi_encode_frame’:
> > libavcodec/a64multienc.c:342:17: warning: ‘buf’ may be used uninitialized
> > in this function [-Wuninitialized]
> >
> > The compiler has trouble to figure out that the if block
> > if (c->mc_frame_counter == c->mc_lifetime) {
> > never should be entered with both values being 0. So add
> > an explicit check on one of the parameters.
> > ---
> > libavcodec/a64multienc.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/libavcodec/a64multienc.c b/libavcodec/a64multienc.c
> > index c9d3b3c..9d3dca5 100644
> > --- a/libavcodec/a64multienc.c
> > +++ b/libavcodec/a64multienc.c
> > @@ -304,7 +304,7 @@ static int a64multi_encode_frame(AVCodecContext *avctx,
> > AVPacket *pkt,
> > }
> >
> > /* lifetime reached so now convert X frames at once */
> > - if (c->mc_frame_counter == c->mc_lifetime) {
> > + if ((c->mc_frame_counter == c->mc_lifetime) && c->mc_lifetime) {
> > req_size = 0;
> > /* any frames to encode? */
> > if (c->mc_lifetime) {
> > --
>
> If this is correct, simpler would be to remove the if (c->mc_lifetime)
> condition on the last line above. However, I do not think this is the
> case, at least it is not equivalent to the current code. If the !pict
> condition is true, mc_lifetime and mc_frame_counter can both be set to
> zero (in a rather convoluted way). This happens if encode() is called
> twice with a null pict parameter, which is normal to flush the delayed
> frames at the end of an encoding. On the second call with null input,
> the encoder will return a zero-sized packet. On the third, it finally
> reports end. This seems somewhat strange, so it may well be an error.
>
> Assuming the final zero-length packet is incorrect, there is a simpler
> solution to it all (untested):
>
> diff --git a/libavcodec/a64multienc.c b/libavcodec/a64multienc.c
> index c9d3b3c..9de5458 100644
> --- a/libavcodec/a64multienc.c
> +++ b/libavcodec/a64multienc.c
> @@ -279,14 +279,10 @@ static int a64multi_encode_frame(AVCodecContext *avctx,
> AVPacket *pkt,
>
> /* no data, means end encoding asap */
> if (!pict) {
> + /* limit lifetime to remaining frames */
> + c->mc_lifetime = c->mc_frame_counter;
> /* all done, end encoding */
> if (!c->mc_lifetime) return 0;
> - /* no more frames in queue, prepare to flush remaining frames */
> - if (!c->mc_frame_counter) {
> - c->mc_lifetime = 0;
> - }
> - /* still frames in queue so limit lifetime to remaining frames */
> - else c->mc_lifetime = c->mc_frame_counter;
> /* still new data available */
> } else {
> /* fill up mc_meta_charset with data until lifetime exceeds */
> @@ -306,8 +302,6 @@ static int a64multi_encode_frame(AVCodecContext *avctx,
> AVPacket *pkt,
> /* lifetime reached so now convert X frames at once */
> if (c->mc_frame_counter == c->mc_lifetime) {
> req_size = 0;
> - /* any frames to encode? */
> - if (c->mc_lifetime) {
> req_size = charset_size + c->mc_lifetime*(screen_size +
> colram_size);
> if ((ret = ff_alloc_packet(pkt, req_size)) < 0) {
> av_log(avctx, AV_LOG_ERROR, "Error getting output packet of
> size %d.\n", req_size);
> @@ -328,7 +322,6 @@ static int a64multi_encode_frame(AVCodecContext *avctx,
> AVPacket *pkt,
> /* advance pointers */
> buf += charset_size;
> charset += charset_size;
> - }
>
> /* write x frames to buf */
> for (frame = 0; frame < c->mc_lifetime; frame++) {
>
> --
probably OK
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